Hi,
The short "// Zugriffsverletzung" or "//
access violation" not enough and not helpful, the full message will be more useful.
Also the stack at this point, because the exact point of the raised
exception is not visible here, it could be FOldWindowProc assigned to some already not allocated memory, hence the
AV, or within the FOldWindowProc and there wasn't debug information and the your debugger showed this point.
And then there is this question :
Are you sure that you need to call "inherited DefaultHandler(Message)" and then reprocess the message again with "FOldWindowProc(TMessage(Message))" ?