nullrefererence exception was unhandled

[Prathap]

nullrefererence exception was unhandled. I'm getting this error. could someone pls help
here is my code
Private Sub Button2_Click(B yVal sender As System.Object, ByVal e As System.EventArg s) Handles Button2.Click
WebBrowser1.Doc ument.GetElemen tById("Email"). SetAttribute("v alue", TextBox1.Text)
WebBrowser1.Doc ument.GetElemen tById("Password ").SetAttribute ("value", TextBox1.Text)
WebBrowser1.Doc ument.GetElemen tById("Signin") .InvokeMember(" Click")
End Sub

[Crusader2010]

Your WebBrowser1.Doc ument does not exist or hasn't been properly defined as an object, or one of the elements (email,password ,signin) don't exist... Or something along those lines