Useful or not, from you.
angular Error after updated to version 9

Trying to update to version 9.

Cryptic errors and massive headache as usual 😱.

I'm stuck on this one:

ERROR in node_modules/@angular/common/http/http.d.ts:2801:22 - error NG6002: Appears in the NgModule.imports of AppModule, but could not be resolved to an NgModule class.

This likely means that the library (@angular/common/http) which declares HttpClientModule has not been processed correctly by ngcc, or is not compatible with Angular Ivy. Check if a newer version of the library is available, and update if so. Also consider checking with the library's authors to see if the library is expected to be compatible with Ivy.

What does it mean?

That's a useful answer
Without any help

@petebacondarwin When I faced the issue I tried to restart several times and each time I got this error.

$ ng serve 
Compiling @angular/cdk/keycodes : module as esm5
Compiling @angular/cdk/platform : module as esm5
Error: Tried to write ...../node_modules/@angular/cdk/platform/platform.d.ts.__ivy_ngcc_bak with an ngcc back up file but it already exists so not writing, nor backing up, ...../node_modules/@angular/cdk/platform/platform.d.ts.
This error may be because two or more entry-points overlap and ngcc has been asked to process some files more than once.
You should check other entry-points in this package and set up a config to ignore any that you are not using.
Error: Tried to write ...../node_modules/@angular/cdk/platform/platform-module.d.ts.__ivy_ngcc_bak with an ngcc back up file but it already exists so not writing, nor backing up, ...../node_modules/@angular/cdk/platform/platform-module.d.ts.
This error may be because two or more entry-points overlap and ngcc has been asked to process some files more than once.
You should check other entry-points in this package and set up a config to ignore any that you are not using.
Error: Tried to write ...../node_modules/@angular/cdk/platform/index.d.ts.__ivy_ngcc_bak with an ngcc back up file but it already exists so not writing, nor backing up, ...../node_modules/@angular/cdk/platform/index.d.ts.
This error may be because two or more entry-points overlap and ngcc has been asked to process some files more than once.
You should check other entry-points in this package and set up a config to ignore any that you are not using.
Compiling @angular/cdk/collections : module as esm5
Compiling @angular/cdk/portal : module as esm5
Compiling @angular/common/http : module as esm5
Compiling @ngrx/store : module as esm5
Compiling @angular/core/testing : module as esm5
Compiling @angular/platform-browser/testing : module as esm5
Compiling @angular/router : module as esm5
Compiling @angular/material/form-field : module as esm5
Compiling @angular/cdk/scrolling : module as esm5
Compiling @angular/cdk/layout : module as esm5
Error: Failed to compile entry-point @angular/cdk/scrolling (module as esm5) due to compilation errors:
node_modules/@angular/cdk/platform/platform-module.d.ts:8:22 - error NG6002: Appears in the NgModule.imports of ScrollingModule, but could not be resolved to an NgModule class.

This likely means that the library (@angular/cdk/platform) which declares PlatformModule has not been processed correctly by ngcc, or is not compatible with Angular Ivy. Check if a newer version of the library is available, and update if so. Also consider checking with the library's authors to see if the library is expected to be compatible with Ivy.

8 export declare class PlatformModule {
                       ~~~~~~~~~~~~~~

Warning: Skipping processing of @angular/cdk/overlay because its dependency @angular/cdk/scrolling failed to compile.
Warning: Skipping processing of @angular/material/select because its dependency @angular/cdk/scrolling failed to compile.
Warning: Skipping processing of @angular/material/dialog because its dependency @angular/cdk/scrolling failed to compile.
Warning: Skipping processing of @angular/material/tooltip because its dependency @angular/cdk/scrolling failed to compile.
Compiling @angular/compiler/testing : module as esm5
Compiling @angular/cdk/text-field : module as esm5
Error: Failed to compile entry-point @angular/cdk/text-field (module as esm5) due to compilation errors:
node_modules/@angular/cdk/platform/platform-module.d.ts:8:22 - error NG6002: Appears in the NgModule.imports of TextFieldModule, but could not be resolved to an NgModule class.

This likely means that the library (@angular/cdk/platform) which declares PlatformModule has not been processed correctly by ngcc, or is not compatible with Angular Ivy. Check if a newer version of the library is available, and update if so. Also consider checking with the library's authors to see if the library is expected to be compatible with Ivy.

8 export declare class PlatformModule {
                       ~~~~~~~~~~~~~~

Warning: Skipping processing of @angular/material/input because its dependency @angular/cdk/text-field failed to compile.
Compiling @angular/material/button : module as esm5
Warning: Skipping processing of @angular/material/paginator because its dependency @angular/cdk/scrolling failed to compile.
Compiling @angular/material/icon : module as esm5
Compiling @ngrx/effects : module as esm5
Compiling ng-block-ui : module as esm5
Compiling @angular/cdk/accordion : module as esm5
Compiling @angular/material/divider : module as esm5
Compiling @angular/cdk/stepper : module as esm5
Compiling @angular/cdk/table : module as esm5
Compiling @angular/material/sort : module as esm5
Compiling @angular/common/testing : module as esm5
Compiling @angular/platform-browser-dynamic/testing : module as esm5
Compiling @angular/cdk/tree : module as esm5
Warning: Skipping processing of @angular/cdk/drag-drop because its dependency @angular/cdk/scrolling failed to compile.
Compiling @ngrx/router-store : module as esm5
Warning: Skipping processing of @angular/material/autocomplete because its dependency @angular/cdk/scrolling failed to compile.
Compiling ngx-window-token : module as esm5
Warning: Skipping processing of @angular/material/bottom-sheet because its dependency @angular/cdk/scrolling failed to compile.
Compiling @angular/platform-server : module as esm5
Compiling @angular/animations/browser/testing : module as esm5
Compiling @angular/cdk/clipboard : module as esm5
Compiling ngx-highlightjs : module as esm5
Warning: Skipping processing of @angular/material/datepicker because its dependency @angular/cdk/text-field failed to compile.
Compiling @angular/common/http/testing : module as esm5
Compiling @agm/core : module as esm5
Compiling @angular/material/card : module as esm5
Compiling @angular/material/badge : module as esm5
Warning: Skipping processing of @angular/material/menu because its dependency @angular/cdk/scrolling failed to compile.
Compiling @angular/material/button-toggle : module as esm5
Compiling @angular/material/checkbox : module as esm5
Compiling @angular/material/expansion : module as esm5
Warning: Skipping processing of @angular/material/sidenav because its dependency @angular/cdk/scrolling failed to compile.
Compiling @angular/material/grid-list : module as esm5
Compiling @angular/material/chips : module as esm5
Warning: Skipping processing of @angular/material/snack-bar because its dependency @angular/cdk/scrolling failed to compile.
Warning: Skipping processing of @angular/material/table because its dependency @angular/cdk/scrolling failed to compile.
Warning: Skipping processing of @angular/material/tabs because its dependency @angular/cdk/scrolling failed to compile.
Compiling @angular/material/icon/testing : module as esm5
Compiling @angular/material/radio : module as esm5
Compiling @angular/material/progress-bar : module as esm5
Compiling @angular/material/list : module as esm5
Compiling @angular/material/slide-toggle : module as esm5
Compiling @angular/material/slider : module as esm5
Compiling @angular/material/toolbar : module as esm5
Compiling @angular/material/stepper : module as esm5
Compiling @angular/platform-server/testing : module as esm5
Compiling @angular/material/tree : module as esm5
Compiling @angular/router/testing : module as esm5
Compiling @angular/material-moment-adapter : module as esm5
Compiling @ngrx/entity : module as esm5
Compiling @ngrx/effects/testing : module as esm5
Compiling @ng-bootstrap/ng-bootstrap : module as esm5
Compiling @ngrx/store/testing : module as esm5
Compiling @ngx-loading-bar/core : module as esm5
Compiling @ngrx/store-devtools : module as esm5
Compiling @nrwl/angular : module as esm5
Compiling angular-in-memory-web-api : module as esm5
Compiling @rxweb/reactive-form-validators : module as esm5
Compiling ng-block-ui/http : module as esm5
Compiling ng-block-ui/router : module as esm5
Compiling ngx-clipboard : module as esm5
Compiling ng-inline-svg : module as esm5
Compiling ngx-daterangepicker-material : module as esm5
Compiling ngx-highlightjs/plus : module as esm5
Compiling ngx-perfect-scrollbar : module as esm5
Compiling ngx-permissions : module as esm5
0% compiling
Compiling @angular/cdk/scrolling : module as esm5

chunk {main} main.js, main.js.map (main) 2.46 kB [initial] [rendered]
chunk {polyfills} polyfills.js, polyfills.js.map (polyfills) 690 bytes [initial] [rendered]
chunk {polyfills-es5} polyfills-es5.js, polyfills-es5.js.map (polyfills-es5) 468 kB [initial] [rendered]
chunk {runtime} runtime.js, runtime.js.map (runtime) 6.15 kB [entry] [rendered]
chunk {styles} styles.js, styles.js.map (styles) 7.74 MB [initial] [rendered]
chunk {vendor} vendor.js, vendor.js.map (vendor) 338 kB [initial] [rendered]
Date: 2020-04-02T07:17:12.873Z - Hash: 97a7e2c6a51c119e4be5 - Time: 8625ms

ERROR in Failed to compile entry-point @angular/cdk/scrolling (module as esm5) due to compilation errors:
node_modules/@angular/cdk/platform/platform-module.d.ts:8:22 - error NG6002: Appears in the NgModule.imports of ScrollingModule, but could not be resolved to an NgModule class.

This likely means that the library (@angular/cdk/platform) which declares PlatformModule has not been processed correctly by ngcc, or is not compatible with Angular Ivy. Check if a newer version of the library is available, and update if so. Also consider checking with the library's authors to see if the library is expected to be compatible with Ivy.

8 export declare class PlatformModule {
                       ~~~~~~~~~~~~~~


I tried to build the project but it's the same thing.

$ nx build
Compiling @angular/cdk/text-field : module as esm5
Compiling @angular/cdk/scrolling : module as esm5
Error: Failed to compile entry-point @angular/cdk/text-field (module as esm5) due to compilation errors:
node_modules/@angular/cdk/platform/platform-module.d.ts:8:22 - error NG6002: Appears in the NgModule.imports of TextFieldModule, but could not be resolved to an NgModule class.

This likely means that the library (@angular/cdk/platform) which declares PlatformModule has not been processed correctly by ngcc, or is not compatible with Angular Ivy. Check if a newer version of the library is available, and update if so. Also consider checking with the library's authors to see if the library is expected to be compatible with Ivy.

8 export declare class PlatformModule {
                       ~~~~~~~~~~~~~~

Warning: Skipping processing of @angular/material/input because its dependency @angular/cdk/text-field failed to compile.
Error: Failed to compile entry-point @angular/cdk/scrolling (module as esm5) due to compilation errors:
node_modules/@angular/cdk/platform/platform-module.d.ts:8:22 - error NG6002: Appears in the NgModule.imports of ScrollingModule, but could not be resolved to an NgModule class.

This likely means that the library (@angular/cdk/platform) which declares PlatformModule has not been processed correctly by ngcc, or is not compatible with Angular Ivy. Check if a newer version of the library is available, and update if so. Also consider checking with the library's authors to see if the library is expected to be compatible with Ivy.

8 export declare class PlatformModule {
                       ~~~~~~~~~~~~~~

Warning: Skipping processing of @angular/cdk/overlay because its dependency @angular/cdk/scrolling failed to compile.
Warning: Skipping processing of @angular/material/select because its dependency @angular/cdk/scrolling failed to compile.
Warning: Skipping processing of @angular/material/tooltip because its dependency @angular/cdk/scrolling failed to compile.
Warning: Skipping processing of @angular/material/dialog because its dependency @angular/cdk/scrolling failed to compile.
Warning: Skipping processing of @angular/material/paginator because its dependency @angular/cdk/scrolling failed to compile.
Warning: Skipping processing of @angular/cdk/drag-drop because its dependency @angular/cdk/scrolling failed to compile.
Warning: Skipping processing of @angular/material/autocomplete because its dependency @angular/cdk/scrolling failed to compile.
Warning: Skipping processing of @angular/material/bottom-sheet because its dependency @angular/cdk/scrolling failed to compile.
Warning: Skipping processing of @angular/material/datepicker because its dependency @angular/cdk/scrolling failed to compile.
Warning: Skipping processing of @angular/material/menu because its dependency @angular/cdk/scrolling failed to compile.
Warning: Skipping processing of @angular/material/sidenav because its dependency @angular/cdk/scrolling failed to compile.
Warning: Skipping processing of @angular/material/snack-bar because its dependency @angular/cdk/scrolling failed to compile.
Warning: Skipping processing of @angular/material/table because its dependency @angular/cdk/scrolling failed to compile.
Warning: Skipping processing of @angular/material/tabs because its dependency @angular/cdk/scrolling failed to compile.
Error: There are still unprocessed tasks in the queue and no tasks are currently in progress, yet the queue did not return any available tasks: ParallelTaskQueue
  All tasks completed: true
  Unprocessed tasks (0): 
  In-progress tasks (0): 
  Blocked tasks (0): 
    at ClusterMaster.maybeDistributeWork (...../node_modules/@angular/compiler-cli/ngcc/src/execution/cluster/master.js:129:27)
    at ClusterMaster.onWorkerTaskCompleted (...../node_modules/@angular/compiler-cli/ngcc/src/execution/cluster/master.js:197:18)
    at ClusterMaster.onWorkerMessage (...../node_modules/@angular/compiler-cli/ngcc/src/execution/cluster/master.js:168:33)
    at ...../node_modules/@angular/compiler-cli/ngcc/src/execution/cluster/master.js:50:95
    at ClusterMaster.<anonymous> (...../node_modules/@angular/compiler-cli/ngcc/src/execution/cluster/master.js:246:57)
    at step (...../node_modules/tslib/tslib.js:139:27)
    at Object.next (...../node_modules/tslib/tslib.js:120:57)
    at ...../node_modules/tslib/tslib.js:113:75
    at new Promise (<anonymous>)
    at Object.__awaiter (...../node_modules/tslib/tslib.js:109:16)
An unhandled exception occurred: NGCC failed.
See "/private/var/folders/9t/6ttybf615csckrl72kbl7_bc0000gq/T/ng-ozlxcn/angular-errors.log" for further details.

That's why I had to clear node_modules to make it work.