JQuery Ajax "invalid label" issue
Had this issue where when I made an ajax call with JQuery 1.5.0, Firebug would throw an error saying "Invalid label".
Searching the net, Stackoverflow gave me an insight to where my problem was lying.
As I was also using JQuery Validator on the same page, my Ajax response was having conflict.
Pointing to JQuery 1.6.0 solved my problem.