iMessage app on MacBook keeps asking for password

All of a sudden I got signed out of iMessage and when i try to turn back on under the preference menu, it keeps asking for my apple id password. I type in the password correctly but each time it keeps on asking me for same password 3-4 times, then stops. But can't log on? Obviously the password is correct since I'm posting here, and verified with iTunes ID, etc.

Any ideas, help??

Thanks