[PROBLEM] Pi Freezes/reboots when trying to OC

[coreflake]

hey everybody !
i just installed the new beta 1.1 , fresh install.
i have one hdd connected trough an external powered usb hub.
Now i'm running the pi on the "xbian" profile in OC settings.
everything works fine this way.
If i try to overclock the pi Xbian freezes/restarts ; before it was no problem.
normally i was running the pi on the high setting (2v overvolt).
did anyone experienced the same problem ?
I needed i can make a debuglog.

Thanks in advance !