System.Runtime.InteropServices.ExternalException When Running Windows Forms Application in Terminal Server

System.Runtime.InteropServices.ExternalException When Running Windows Forms Application in Terminal Server

Article ID : 953389
Last Review : May 20, 2008
Revision : 1.0
Source: Microsoft Support

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RAPID PUBLISHING ARTICLES PROVIDE INFORMATION DIRECTLY FROM WITHIN THE MICROSOFT SUPPORT ORGANIZATION. THE INFORMATION CONTAINED HEREIN IS CREATED IN RESPONSE TO EMERGING OR UNIQUE TOPICS, OR IS INTENDED SUPPLEMENT OTHER KNOWLEDGE BASE INFORMATION.

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Action

You are running a Microsoft .NET Framework 2.0 Windows Forms application in a Terminal Server session. You then minimize the termial server session window, disconnect from the session, or lock the session.

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Result

When resuming work in the terminal server session, the Windows Forms application displays the following exception and call stack:

System.Runtime.InteropServices.ExternalException: A generic error occurred in GDI+.
   at System.Drawing.Graphics.Clear(Color color)
   at System.Windows.Forms.ToolStripProfessionalRenderer.OnRenderToolStripContentPanelBackground(ToolStripContentPanelRenderEventArgs e)
   at System.Windows.Forms.ToolStripProfessionalRenderer.OnRenderToolStripContentPanelBackground(ToolStripContentPanelRenderEventArgs e)
   at System.Windows.Forms.ToolStripRenderer.DrawToolStripContentPanelBackground(ToolStripContentPanelRenderEventArgs e)
   at System.Windows.Forms.ToolStripContentPanel.OnPaintBackground(PaintEventArgs e)
   at System.Windows.Forms.Control.PaintWithErrorHandling(PaintEventArgs e, Int16 layer, Boolean disposeEventArgs)
   at System.Windows.Forms.Control.WmEraseBkgnd(Message& m)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.ScrollableControl.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

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Cause

This is due to a bug in the Microsoft .NET Framework 2.0. The Windows Forms run-time is attempting to call System.Drawing.Graphics.Clear without checking to see if it is running on a secure desktop. As documented in the following MSDN link, if the Clear method is called on a secure desktop in a terminal server session, an ExternalException may occur, leaving the Graphics object in an inconsistent state.

Graphics.Clear Method

http://msdn.microsoft.com/en-us/library/system.drawing.graphics.clear.aspx (http://msdn.microsoft.com/en-us/library/system.drawing.graphics.clear.aspx)

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Resolution

You can work around this behavior by wiring an event handler to the Application.ThreadException event. This event allows your application code to handle otherwise unhandled exceptions that occur in Windows Forms threads. This would allow your code to be called instead of the standard Windows Forms exception dialog being displayed.

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
   AddHandler Application.ThreadException, AddressOf Application_ThreadException
End Sub

Sub Application_ThreadException(ByVal sender As Object, ByVal e As System.Threading.ThreadExceptionEventArgs)

   If TypeOf (e.Exception) Is System.Runtime.InteropServices.ExternalException Then
      Return
   End If
   MessageBox.Show(e.Exception.Message, Me.Text)
End Sub

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APPLIES TO
• Microsoft .NET Framework 2.0
• Microsoft .NET Framework 2.0 Service Pack 1 (x86)
• Microsoft .NET Framework 3.0
• Microsoft .NET Framework 3.5

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Keywords: 
kbnomt kbrapidpub KB953389

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Microsoft Knowledge Base Article

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