well i was in a server, played a round, it changed maps then once it had loaded the nextmap it popped up, I tried to rejoin and I got in and halfway through the round I got dropped again, same message
This happens to me when my bro plays CS as well on a different comp (using same account). When my bro plays on a VAC server and i play on a non-secure server, its fine.
I've found by un-checking the 'Remember password' box, i dont get kicked (as much) while my bro plays.
So maybe some1 else is using ur account? (known or unknown).