Programatically Uncheck ToolStripMenuItems

I have several different type of picture formats that the user can select using a check in each menuitem.   An Addhandler is used in Form1.Load to trigger the MyMenuClick subroutine.   Thus far, however, the code hangs in the CheckMenuItem function on the "m.checked = checked" line.   For some reason, it is challenging to uncheck and check toolstripmenuitems -- so am I leaving out a CType (cast) or do I need a sender.sourcecontrol?

Private Function checkMenuItem(ByRef m As ToolStripMenuItem, ByVal checked As Boolean)
If m IsNot Nothing Then
     m.Checked = checked   'hang occurs on this line
     Return True
Else
     Return False
End If
End Function

Private Sub MyMenuClick(sender As Object, e As EventArgs)
        checkMenuItem(WmfToolStripMenuItem, False)
        checkMenuItem(JpgToolStripMenuItem, False)
        checkMenuItem(GifToolStripMenuItem, False)
        checkMenuItem(TifToolStripMenuItem, False)
        checkMenuItem(BmpToolStripMenuItem, False)
End Sub

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