Hopefully you might find the following useful, it is a workaround for the problem I've had with debugging within windows (and sound similar to the issue you have had)...
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Dialog Displayed - Error
Project raised exception class 'External: SIGSEGV'
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Click 'OK'
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Dialog Displayed - Execution Paused
Adress: $7C918FEA
Procedure ntdll!RTLPWaitForCriticalSection
File:
(Some day an assembler window might popup here

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Click 'OK'
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Generate or remove a breakpoint - doesn't matter where (have tried in both a unit or the lpr file) I tend to use the lpr file but either seem to work fine.
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Dialog Displayed - Execution Paused
Adress: $7C901231
Procedure ntdll!DbgUiConnectToDbg
File:
(Some day an assembler window might popup here

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Click 'OK'
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Unpause the application (toolbar or menu seems to work fine).
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It seems to work fine (for me at least) after this - debugging working as expected (though the project window does sometimes appear behind the form).
Kind Regards,
Steven Coombs