Until someone comes up with a solution you can try eliminating some of the sources of error like trying Ufasoft Miner - https://bitcointalk.org/index.php?topic=3486.0
or picking another pool.
600 kh/s is not a lot, and I know that some pools disconnect users/workers who submit a very low number of shares in some timeframe, but I have no idea if DeepBit is one of them?