Make sure the @angular/animations package is installed (e.g. by running npm install @angular/animations). Then, in your app.module.ts

import { BrowserAnimationsModule } from '@angular/platform-browser/animations';

@NgModule({
  ...,
  imports: [
    ...,
    BrowserAnimationsModule
  ],
  ...
})

This error message is often misleading.

You may have forgotten to import the BrowserAnimationsModule. But that was not my problem. I was importing BrowserAnimationsModule in the root AppModule, as everyone should do.

The problem was something completely unrelated to the module. I was animating an*ngIf in the component template but I had forgotten to mention it in the @Component.animations for the component class.

@Component({
  selector: '...',
  templateUrl: './...',
  animations: [myNgIfAnimation] // <-- Don't forget!
})

If you use an animation in a template, you also must list that animation in the component's animations metadata ... every time.

I ran into similar issues, when I tried to use the BrowserAnimationsModule. Following steps solved my problem:

1. Delete the node_modules dir
2. Clear your package cache using npm cache clean
3. Run one of these two commands listed here to update your existing packages

If you experience a 404 errors like

http://.../node_modules/@angular/platform-browser/bundles/platform-browser.umd.js/animations

add following entries to map in your system.config.js:

'@angular/animations': 'node_modules/@angular/animations/bundles/animations.umd.min.js',
'@angular/animations/browser':'node_modules/@angular/animations/bundles/animations-browser.umd.js',
'@angular/platform-browser/animations': 'node_modules/@angular/platform-browser/bundles/platform-browser-animations.umd.js'

naveedahmed1 provided the solution on this github issue.