Error opening messages in outlook expres

I have a client running NT 4.0 workstation and the Sabre travel program.
Problem is they can receive mail but when they try to open it, it pops up a message stating an error opening message reload express, when they try to send a new message it pops up with fail to load address book, express it configured incorrectly, reconfigure.
Any ideas? We have tried to relod Express 4 times with no success, we cannot reload NT because of Sabre travel program