Actually, you are using build 12, so you'll want to get the release version at markspace.com/downloads.html (sorry, I still can't post full URLs on this site)
We're getting the NIL error when we encounter a data type we aren't suspecting. You mentioned it was working fine for a while, but now it's not. Did you sync with a PC just prior to it not working on the Mac?
Please let me know.