First, make sure you un-checked "Old IC2 Access Method" during installation (it ain't for X1K cards). Currently I assume it is installed, so, un-install it, and just re-install it to un-check that option.
Second, if you aren't over-clocking it via ATi Tray Tool then make sure you disable "ATT Shared Memory".
Try and see if it helps. If not I have no ideas why it does that.
Edit: Sorry, double post, stupid lag.