Cannot login to Yahoo Messenger 9 - Yahoo Messenger 8 acting up

Our sysadmin at the company where I work recently made some changes to the back end, possibly affecting yahoo messenger, something I need to confirm via this forum.
I had yahoo messenger ver 9 installed on my comp. I have not been able to log in - I changed the settings to use proxy - entered the proxy server and the port address that we use to access the internet. This has not worked.
I uninstalled ver 9 and installed ver 8, and the results have been strange. For one of my addresses, I can login without issues using wither the "firewall without proxies" and "use proxies options". For another address, it logs in and then Yahoo reports incorrect password/username. Minimise this window and I see myself signed in but none of my messenger chat contacts are visible. This is all rather frustrating.
My questions:
(1) How can I get YM 9 to work - especially since I cannot log in even after I have selected use proxy option, and entered the proxy server name and port
(2) Why would ver 8 be acting up on one account and not for the other? For bith I do get the upgrade notification.
Thanks for your help