CDialog::PumpMessage hangs (endless WM_PAINT?)

Question

I have the following weird problem on customer's computer (I cannot look in there and debug): OS: WinXP Application: MFC app on Visual C++ 6 There is a simple CDialog-based dialog that always worked OK. But on one of customer's computers the dialog hangs as soon as it is called. I managed to gather dump on it, and this is what I see in Call Stack:

ntdll.dll!_KiFastSystemCallRet@0()  
user32.dll!_NtUserDispatchMessage@4()  + 0xc bytes  
user32.dll!_DispatchMessageW@4()  + 0xf bytes   
mfc42u.dll!CWinThread::PumpMessage()  + 0x3a bytes  
mfc42u.dll!CWnd::RunModalLoop()  + 0xc6 bytes   
mfc42u.dll!CDialog::DoModal()  + 0xc7 bytes 

If I understood memory dump right, the message id is WM_PAINT. So the dialog probably receives endless WM_PAINT messages and is busy redrawing itself. Why is that? As I said, this is simple About dialog that worked well million times.