I shouldn't have to reboot to fix this... I went from dual monitors to single display and after parallels moved over to my main display I can now no longer choose "View > OS Window" it is GRAY OUT. Why? Parallels 3188, Win XP SP2 with 256mb RAM, running on MBP 1.83gHz with 2gb RAM
What view are you currently in? & have you tried selecting another view and then is it still greyed out after changing?