[LTC] High Percent of Rejected Shares

[magixx]

I've noticed that I am getting a very high amount of stale shares with my HD5830s and I don't really know what it could be, my GPU settings seems reasonable based on the Mining Chart and my router load is low. I'm getting about 290K per card which seems accurate for the settings but I would have thought I could get even more and even with this setup I am getting many rejections of unknown-work or prevhash-stale or prevhash-wrong.

Code:

cgminer settings:
--api-network --api-listen --scrypt -o kattare(I use it due to US location) -u u -p p --thread-concurrency 5728 --gpu-engine 890 --gpu-memclock 1205 --lookup-gap 2 --shaders 1120 --autofan -I 18 -g 1 -w 256

Temperatures are <80*C
My set up is Ubuntu 11.04 x64 11.11 Drivers and 2.5 APP SDK and cgminer running on 4GB USB 2.0 drive.t

What can I change to stop getting so many rejections?

[Waam]

Are using stratum?

[magixx]

I switched over to give-me-ltc which has stratum and that fixed everything.