These past few days I've had issues connecting to Yahoo! Messenger with Pidgin. Getting a bit fed-up, I decided to check the Pidgin bug tracker to see if there was solution in the works.
Indeed, the answer to my connection issue was pretty simple. As referenced in ticket #8853, chaging the Paging Server for Yahoo! under the advanced account options worked for me. I changed it to this:
I hope this issue gets resolved permenently for Pidgin. Although I know they are always playing a cat and mouse game with the official Yahoo! client.