[missing] Digital Cinema Desktop Preview

Hi all.. I suddenly get the message [missing] Digital Cinema Desktop Preview" listed in A/V devices- no hope of going fullscreen it seems. My only other choice is "none". Is there some code I can add or delete somewhere that can help it recognize the Digital Cinema Desktop Preview once again?

I Tried F12. It all used to work just fiine. Instantlyish went to full screen. Now the option is gone...
I have Intel Imac running 10.4.10. FCP 4.5HD.
Could it be a quicktime problem? (now running 7.2.0)??
Can anyone help me please?
Wayne