I have been monitoring the packets from the startum a bit, and I found out that sometimes the pool gives you the same job in a row and thats why there are many rejects.

Here is also my log from cgminer :

 [19:56:24] Rejected 4fb672da Diff 822/512 GPU 1 Pool 0 (Job '3' not found)
 [19:56:31] Rejected 5860ba1b Diff 742/512 GPU 1 Pool 0 (Job '3' not found)
 [19:56:33] Rejected 1647199e Diff 2.94K/512 GPU 0 Pool 0 (Job '3' not found)

Basicly its the same job and it was handed out 3 times.
If you can have a look at this, it might decrease the reject ratio.