I'm not at the computer that had the issue, but we found the problem in the "parallels.log" file in the /Library/logs folder -- you can view this in the Console utility. If you look in that file as you go to register, you can see it getting an error trying to write to a preferences file. (I don't remember the name, but it's in the log file.) We tried fiddling with permissions on that file and its folder, but that didn't help. We deleted the preferences file, and the program tried to recreate it, but it was still bad (I think the program was creating a new bad one?). He copied one from his computer -- which I assume was good -- and when I went to register, it was able to write just fine to it. Since then all has been good.