Welcome to the X-Cart forums! Please start by reading the following thread, which will help you get started and hopefully make your experience here a positive one:
http://forum.x-cart.com/showthread.php?t=23970
Please note that this link is not an answer to your question, but we need you to update your signature with your X-Cart version so that we can answer your question correctly.
I have also moved this thread to its own thread in the Third Party Add-Ons forum, as the thread you posted in was for setting up FedEx in X-Cart, not a third party solution. You should contact Adam at RubyMods first and try to resolve the issue that way before posting in the forums.