This problem has already been reported and closed as fixed here :
Unfortunately this problem still occurs in VS 2012 RTM (.Net 4 project, x64 configuration)
My system configuration is : Windows 8 Pro RTM + VS 2012 RTM
What I've noticed is that this bug might have something to do with Cisco VPN client (running Cisco AnyConnect VPN Client Version 2.5.2001)
Whenever I connect to the corporate VPN I seem to be getting the error. It occurs until I restart the machine. After rebooting everything goes back to normal.
If I start VPN connection during the debugging session running I get VS to show dialog saying : "Remote operation takes longer than expected" followed by message box with error "The debugger's worker process (msvsmon.exe) unexpectedly exited. Debugging will be aborted.". When I try to start debugging again I get the error mentioned before. ("Cannot start or attach debugger...")