I have two suggestions:
are you running applications compiled with vfp 6 and vfp 7 on the same machine? I have found that the error appears more often in this case, and only running the vfp-7 compiled app. If this is the case, even with resource set to OFF, delete the resource file just before starting your vfp7 app.

does the error appear often when you CLOSE the preview window? In this case, try to exit the preview using the form close button (i.e. x in right upper corner) and do NEVER use the exit door in the preview bar.

These two things reduced greatly the frequency of c5s in my case.

NOte: if the error has appeared ONCE, restart the machine before trying any other approach.