Dean,
Essentially what is happening is that when you run the command:
powercfg -requests
whatever shows up in the [DISPLAY] section of that output is the culprit.
What Tai is suggesting is that you take whatever that process is and override it with the following:
powercfg -requestsoverride PROCESS <insert offending process> DISPLAY
This should release whatever lock that process has on the display and will allow the screensaver and whatever screen-based system actions to take place.