Just downloaded the upgrade to version 4.0 for ListPro a couple of days ago and have had a couple of Fatal Exceptions since. Both times this happened when I left the palm side in ListPro when I closed the phone, then went directly from ListPro to the phone side when I reopened it. I can't recreate it at will though.

Just a caution if you use ListPro a lot because the upgrade converts your list files to a new format. When installing, choose the option for backing up your lists (might do it automatically - can't remember ) so you can go back to version 3 if necessary.