In a Delphi 7 project we installed FastMM. Soon after that we noticed one of the forms started to issue Abstract Error message on close. I have debugged this extensively and I can't find the reason so far. The usual reason for this error message doesn't seem to apply here. The application doesn't define abstract classes. I also searched the form for a possible use of TStrings or something like that. Most importantly, we didn't (well, we think we didn't) make any changes to this form. It just broke.
If the answer to these questions is no, then I'll just continue to search for an unimplemented method call, relieved that I am not missing something else.
If there is memory corruption then all sort of errors can be raised and it is very difficult to find the cause.
To answer your questions: 1) Yes abstract error can also be caused by memory corruption, and 2) Yes enabling FastMM can make bugs visible that normally pass unnoticed (but should still be fixed).
Some general advice for finding memory errors: