MESSENGER FOR MAC?

Ok, i have a question... I have messenger for mac in both macs ( macbook, imac) when i open messenger in my macbook it works ok! but when i go to my imac, and log in in messenger all of the sudden all my contacts are blocked and it ask me if i want to allow all my contacts to see me... this thing happens in my office again with the same account but not in my macbook pro.... anybody knows why or can help me?
i already try several options but nothing.... i uninstalled and installed again but nothing... so help me out!