I have a samsung galaxy tab 10.1, I had the saem problem with not being able to sign into the app on my tab with android 3.0 and even after the update to 3.1. It turns out that my time zone was not correct. Fixed that and then i still could not sign in, look at my time and it reset my time back a few hours since my tab was originally on gmt. so set the time correctly and shebang it worked.
So make sure your time zone and time are correct for your area.