It seems that sometimes applications that install a keyboard hook (to monitor media keys, for instance) can randomly stop receiving the keyboard commands. I’ve seen this problem happen with the Groovie app. I’ve also heard of it happening with various music and video players.
It turns out to be a bug in Windows7; under full-load, the Operating System will not allow sufficient time for the hooks to process the messages and will remove them without notifying the application.
One workaround that I found was to increase the Hooks Timeout setting in the Windows registry:
Go to HKEY_CURRENT_USER\Control Panel\Desktop and set the LowLevelHooksTimeout to a larger value, I used 2710 (which is 10 seconds)
Hope this helps someone.