Beter posted in the Software - Instant Messaging section...
Anyway, check the following points:
Faulty installation: Uninstall. Download new Yahoo! messager ONLY FROM the Yahoo! site. Reinstall.
(some other sources MAY NOT be reliable and may contain some maleware)
Check that all configuration items are properly set.
I realy don't think that there is a "side to side" configuration.
More chances for that to be "Site to site" or "Peer to peer" (P2P) configuration.
Also check that your firewall is properly set to allow Yahoo! messenger to access the internet.
Electro, July 2011
