formGroup expects a FormGroup instance

I was facing this issue and fixed by putting a check in form attribute. This issue can happen when the FormGroup is not initialized.

<form [formGroup]="loginForm" *ngIf="loginForm">
OR
<form [formGroup]="loginForm" *ngIf="this.loginForm">

This will not render the form until it is initialized.

I had a the same error and solved it after moving initialization of formBuilder from ngOnInit to constructor.

I was using reactive forms and ran into similar problems. What helped me was to make sure that I set up a corresponding FormGroup in the class. Something like this:

myFormGroup: FormGroup = this.builder.group({
    dob: ['', Validators.required]
});

There are a few issues in your code

• <div [formGroup]="form"> outside of a <form> tag
• <form [formGroup]="form"> but the name of the property containing the FormGroup is loginForm therefore it should be <form [formGroup]="loginForm">
• [formControlName]="dob" which passes the value of the property dob which doesn't exist. What you need is to pass the string dob like [formControlName]="'dob'" or simpler formControlName="dob"

Plunker example