Problem:
Full screen option disappeared (cannot choose toggle full screen)

Solution:
They may have somehow turned off the DirectDraw Overlay setting under System Configure.

If it is this, to resolve do the following
1) Setup --> System Configure
2) Make sure that Enable DirectDraw Overlay is ticked.
3) Restart Multicam software

Note: Only separated VGA card can support DirectDraw Overlay and there is no such feature with onboard VGA