sorry to hear that.  0.5 added a "feature" called mother which when a card locks up it reboots the server and disables OC on that card.  It is posisble that it what happened.

I use cgminer and really just use BAMT for the OS.  I find it more stable and easier to configure that way. 

Still I am considering offering a bounty for a cgminer only OS as BAMT doesn't support x64 and thus is limited to 6 or 7 GPUs per rig.