Ok, my girl and I each have an early 2011 MBP running OSX 10.7.3. Normally Airdrop works ok, but every now and then it doesn't work, and my girl and I each have to force quit finder and relaunch which normally fixes the problem. Lately when we try and use Airdrop, I get this error message when trying to send anything "The Apple ID certificate for Artnotwar's girl is invalid. The transfer has been canceled." If anyone can come up with a solution to get my Airdrop working again I would be more than happy.