Please Help AOL Instant Messanger problems

AOL Instant Messanger worked on windows 98 just fine but can't get it to work on windows xp it goes to sign and then it come up with a error code it is ------ unknown error------- error catagory 4----- error code 1 if any one can help it would really help. I also contacted AOL and they told me to uninstall and reinstall and it will work but no luck. Some say running a firewall has something to do with it . I am running a firewall. PLEASE HELP Thanks.