Have a look at post #4 in the following thread which directs you to the event viewer in Windows. You might find something similar in the records.

I thought I'd fixed it by changing the USB port my pendant was plugged into but then it happened again and I gave up trying to fix the problem on the laptop and reverted to using an old W7 desktop machine which has been rock solid ever since. You could also have a look at the UCCNC forum.

http://www.mycncuk.com/threads/14698...n-unexpectedly