That's on google's side... they think you're a robot. 
We've had luck with the following fixes... give one or more of these a try and see if it takes care of you.

a) clear your cache and cookies (ctrl-H --> clear cache and cookies for the last 24 hours)... that fixes this about 75% of the time
b) wait a little while and try again
c) go to ... it should ask you if you're a robot (i don't remember what it looks like exactly, but will make you check a verification box or click on all the pictures with cars or something like that). Once you verify with google that you aren't a robot, it should work.