5850 OC works unter Windows but not under Ubuntu

[TAiS46]

Hello,

I have install today Ubuntu.

On Windows 7 I oc my two 5850 to 850/300
Now I am trying to oc the 5850 unter ubuntu with atitweak: atitweak -e 850 -m 300

But my system is only freezing!
I have also try 800/300 but it will also freeze.

Why? Can somebody give me some hind?

I have the newest driver of ati installed.

Thank you

[TAiS46]

okay, i have solve it! have not installed the correct driver