Thunderbird Portable wont start

I have Thunderbird portable on a usb stick and until yesterday have had no problems. This version travels between my win xp machine at work and a vista machine at home. Yesterday Thunderbird would not start on the XP machine but will run fine on the Vista machine. I tried re-install of the portable app but no change. The error I get is a non-specific error "thunderbird.exe has encountered a problem and needs to close. We are sorry for the inconvenience." I also have Firefox portable on the same usb stick and it works fine. Can anyone help?
Thank you
Adam