First of all, thanks to everyone for all the help.

> You need to build a VM using an image at change set 4649 or higher 

This would have posed a major problem for me, as this all started
because I wanted to be able to load update #4640 (or an image containing
it) without crashing.

But I was able to get 4640 to file in with a small tweak -- I eliminated
the change to the method FormCanvas>>contentsOfArea:into:. It turned out
this was causing the crash. Hopefully, after I get a successful vm
build, I will be able to run with the updated version of that method. In
the meantime, the image seems to run without the change to that method
(knock on wood!).

I'll try what you suggested, and also Robert Withers suggestion if that
fails. 

Thanks again.