msn messenger problem with squid

Dear All
I m running Linux Proxy Server on RHEL-5 64bit for providing http access to users in my office, i m facing a problem while using msn messenger on LAN, we access msn messenger through above mentioned proxy server, whenever I sign in to msn messenger, it gets signed on but after a short while it gets signed out automatically and shows message "your connection with windows live messenger has been lost reconnecting" i have removed all the acls on squid which were blocking msn msgr even then i m unable to solve this problem, i have put some acls to access msn messenger but in vain, when i test proxy and ports on msn msgr it sticks on key ports and shows error, plz tell me which ports msn uses and what to do on proxy server end solve this problem which is a headache for me now

I ill really appreciate your cooperation

Thanks

please help me on the above issue

thanks