Or get GroupTool (Look at Brandon Wilson's author profile at ticalc.org) I've successfully ungrouped such files with it.
I've come to think that this is the reason for my massive Serenity corruption, as I used it frequently before, and since I stopped using it, have not had the problem again. I ruled out TiConnect, because files that I had not transferred to my computer were later found to be corrupted too

Anyway, I've stopped using GroupTool, even though it is very very usefull.