...
Please use another miner (I recommend phoenix or poclbm).
Hmm... something is wrong with your pool.
Using cgminer or even the latest phoenix, which i turn you do recommend, gives a very high reject ratio. Here a sample of phoenix:
[11/08/2011 22:10:40] Result: 8de61579 accepted
[11/08/2011 22:10:40] Result: 5db3749b accepted
[11/08/2011 22:10:53] Result: 8d544c0e rejected
[11/08/2011 22:11:04] Result: 2c6441e8 accepted
[11/08/2011 22:11:19] Result: 96316e6b accepted
[11/08/2011 22:11:48] Result: 538cf092 rejected
[11/08/2011 22:11:59] Result: b54181b1 rejected
[11/08/2011 22:12:30] Result: 2e4c4c9c accepted
[11/08/2011 22:12:33] Result: d3539822 accepted
[11/08/2011 22:12:58] Result: 281068ea accepted
[11/08/2011 22:13:05] Result: c8aa1ac6 rejected
[11/08/2011 22:13:24] Result: 51fb1ca1 rejected
[11/08/2011 22:13:31] Result: 37c7b8e4 accepted
[11/08/2011 22:13:33] Result: 66ceb98a rejected
[11/08/2011 22:13:58] Result: a8ae8e09 accepted
[11/08/2011 22:14:03] Result: 820cb009 rejected
[11/08/2011 22:14:04] Result: 6193ed32 accepted
[11/08/2011 22:14:14] Result: 22feb555 accepted
[11/08/2011 22:14:22] Result: 5318a11a rejected
[11/08/2011 22:14:23] Result: e61b1c56 accepted
[11/08/2011 22:14:25] Result: f3cd4c22 accepted
[11/08/2011 22:14:26] Result: fb35e3df accepted
[11/08/2011 22:14:31] Result: db9690de rejected
[11/08/2011 22:15:03] Result: b2d6b790 accepted
[11/08/2011 22:15:09] Result: 57159855 rejected
[11/08/2011 22:15:22] Result: 1b373f95 accepted
[11/08/2011 22:15:24] Result: a134167c accepted
[11/08/2011 22:15:40] Result: 09c99be7 accepted
[11/08/2011 22:15:43] Result: a6f5f619 accepted
[11/08/2011 22:15:50] Result: fc2c5c20 accepted
[11/08/2011 22:16:01] Result: 7c495db8 accepted
[450.57 Mhash/sec] [54 Accepted] [10 Rejected] [RPC]
Your pool works well only with poclbm but with poclbm I have over 20Mhases/sec less. I don't know what is wrong with your pool, but it occurs only mining with your pool. Btcguild, deepbit, arsbitcoin, eligius and other smaller pools, all are working very well with reject ratios about or less than 1 percent.