FYI:
I recently ran into a problem where the C0000005 error would arise after closing a particular data entry form -- sometimes immediately, sometimes a few actions (clicks, other forms, etc.) later. The error message itself would note one of several different procedures as the offending LOC. In other words, an inconsistent offending LOC. The form in question is a secondary form called from a main data entry form, all of which is built on an in-house framework. Other secondary forms based on the same class generated no problems, but this form would -- albeit inconsistently. I tried everything I could to make sure the object and data architecture of the form was exactly like the other forms (that did not generate the error), but nothing seemed to alleviate the intermittent bug (my favorite kind...). Totally disgusted, I blew away the old form and recreated it from scratch using the exact same classes and every line of code as the original. Now it works fine. Of note is the fact that the form was originally developed in VFP7 and had two third-party list controls (OLE objects) on it. Those had been replaced with VFP listboxes during the migration to VFP8. Apparently, there was some residual "oop goop" in the SCX that was not cleared out when the objects were replaced...or something. I had even tried browsing the SCX as a table, but found nothing out of whack.

Bottom line is, if you're having a similarly evasive C5 error in a form, you may want to recreate the form from scratch.