I spent hours looking at certificates, connections, etc., and finally found something that worked for my MacBook Pro running 10.7.5, found here. Instantly fixed my connection issue and I logged right in. FINALLY.
August 7th, 2012, 12:57 PM#9
After trying all of the fixes in this blog and a few others outside of this blog, I was ready to erase/reboot the entire computer. And, then... I noticed that the computer date was set incorrectly. I reset the date, and everything worked perfectly.
Note: I'm not sure if the date, along with the certificate reset and cache clear (in combination) helped, but until I changed the date to reflect the actual date/time, the other fixes didn't work.