I have an angular routing , in one of the component i have simple login form and provide the formGroup in template ,which shows above error.
Steps: Import the ReactiveFormsModule in app module.
In Routing components:
app.routingmodule.ts
import { RouterModule } from '@angular/router';
import { NgModule } from '@angular/core';
import { LoginViewComponent } from './views/login/login.component';
import { HomeViewComponent } from './views/home/home.component';
import { CatalogViewComponent } from './views/catalog/catalog.component';
@NgModule({
  declarations: [ 
    LoginViewComponent, HomeViewComponent, CatalogViewComponent
  ],
  imports: [
    RouterModule.forRoot([
      { path: 'login', component: LoginViewComponent },
      { path: 'home', component: HomeViewComponent },
      { path: 'catalog', component: CatalogViewComponent },
      { path: '**', redirectTo: 'login' }
    ])
  ],
  exports: [
    RouterModule
  ],
  providers: [],
})
export class AppRoutingModule {}
catalog.component.ts
import { Component, OnInit } from '@angular/core';
import { Http } from '@angular/http';
import { FormControl, FormGroup } from '@angular/forms';
@Component({
  selector: 'reactiveform',
  templateUrl: 'catalog.component.html',
})
export class CatalogViewComponent implements OnInit {
  form: FormGroup;
  constructor() {
  }
  ngOnInit() {
    this.form = new FormGroup({
      name: new FormControl(''),
      userName: new FormControl('')
    });
    console.log(this.form);
  }
  processForm() {
    console.log("formProcessing" + this.form.value);
  }
}
catalog.component.html
<form [formGroup]="form" (ngSubmit)="processForm()" >
    <div class="form-group">
        <label for="name">Name </label>
        <input type="text" class="form-control" name="name" formControlName="name" required>
    </div>
    <div class="form-group">
        <label for="userName">Username </label>
        <input type="text" class="form-control" name="userName" formControlName="userName" required>
    </div>
    <div class="form-group">
        <button type="submit" class="btn btn-danger">Submit   </button>
    </div>
</form>
Demo URL:
If I remove the formGroup in Html, the application works fine