I'm using this code to determine if an instance of the form is already open, but I get an error...any suggestions?

Code:
Dim frmdataentry1 As frmDataEntry = Nothing
        If frmdataentry1 Is Nothing Then
            frmDataEntry1 = New frmDataEntry()
            frmDataEntry1.MdiParent = Me
            frmDataEntry1.Show()
         End If

Additional information: The form that was specified to be the MdiParent for this form is not an MdiContainer.