I ran into this problem myself when I upgraded to VFP8. I posted the problem here on the UT. To determine what object was causing the problem, I started with a new blank form and added to it the objects from the problematic form one by one and tested the form until it bombed. It turned out that it was a problem in the caption of one of the labels on my form. I was using the syntax

caption = "="

without a space before the = sign and changing it to:

caption = " ="

with a space before the equal sign fixed the problem. Someone on the UT helped me out with this.