Try the newer v7 client and see if you still get the "UNSTABLE_MACHINE" errors.
Also are you using both 260's in the rig? If you are, you need to extend the 2nd card to the 1st that way the client will see both cards.
“I have pretty much own every card known to man. what should I use?” -W1zzard
My F/S Thread
“I quit smoking pot a while ago.. but not today” -erocker