Hi, I developed an application that has a form (1st form) with a button. when I press the button another form (2nd form) is displayed which has a button too. when I press this button another form (3rd form) is displayed and then when I close this form the 2nd form is showed again but immediately 'System.InvalidOperationException' is occurred with the following message: Invoke or BeginInvoke cannot be called on a control until the window handle has been created. I use the following codes for showing and closing the forms: frm2 obj2 = new frm2(); obj2.ShowDialog(); this.Close(); There is a ReportViewer in the 3rd form that works fine. Thanks in advance for any help to resolve the exception.