Spontaneous NullReferenceException in System.Windows.Forms

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In our .NET Framework 1.1 Application that is installed on about 800
PC's we have 5 PC's that has spontaneous NullReference Exceptions
(Windows XP & 2000 uptodate) in System.Windows.Forms. We already
removed any Crossthread Calls. Reinstalling and replacing the computer
hasn't brought us any better results. In some cases this exception only
appears twice a week, sometimes 20 times a day depending on workingday
or / and computer. Here are the two different call stacks (sometime it
appears also with SetActiveCore:

Stack Trace:
at System.Windows.Forms.UnsafeNativeMethods.PeekMessage(MSG& msg,
HandleRef hwnd, Int32 msgMin, Int32 msgMax, Int32 remove)
at
System.Windows.Forms.ComponentManager.System.Windows.Forms.UnsafeNativeMethods+IMsoComponentManager.FPushMessageLoop(Int32
dwComponentID, Int32 reason, Int32 pvLoopData)
at System.Windows.Forms.ThreadContext.RunMessageLoopInner(Int32
reason, ApplicationContext context)
at System.Windows.Forms.ThreadContext.RunMessageLoop(Int32 reason,
ApplicationContext context)
at System.Windows.Forms.Application.RunDialog(Form form)
at System.Windows.Forms.Form.ShowDialog(IWin32Window owner)
at System.Windows.Forms.Form.ShowDialog()


Stack Trace:
at System.Windows.Forms.SafeNativeMethods.ShowWindow(HandleRef hWnd,
Int32 nCmdShow)
at System.Windows.Forms.Control.SetVisibleCore(Boolean value)
at System.Windows.Forms.Form.SetVisibleCore(Boolean value)
at System.Windows.Forms.Form.ShowDialog(IWin32Window owner)
at System.Windows.Forms.Form.ShowDialog()

 

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Is there a possibility that it appears, because the .NET Framework 1.1
and 2.0 are installed on these computers? We already placed a config
file, so the application only will be executed on 1.1!

 

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It's not the .net framework 2.0. But we can now say that the problem
occurs, if a form is closed (perhaps after closing access to a
usercontrol??) Isn't ther anyone that has the same problem?

 

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Everytime I search in the newsgroups and on the web I get more search
results, with similar problems, without any solutions. Dear Microsoft,
why don't you answer these questions?