This was reported in another post, and this fix (by Rogelio Agua) worked for me:
http://forums.creativecow.net/readpost/14/863108
1. Launch your Quicktime Player.
2. Go to Edit/Preferences/Quicktime Preferences/Advanced.
3. Under Video, change from Direct X to Safe Mode (GDI only)
4. Close the QT Player, then launch Combustion and in the Render menu, pick Quicktime under Format, then click the Options button. It should work now.
I've seen this problem twice -- once a few months ago, and now just a couple of days ago. Most recently, it occurred after I'd both installed a new version of Quicktime AND installed new Nvidia graphics drivers for my video card (EVGA 7800 GT.) I think it's a combo Combustion/Quicktime bug with Direct X, so try the above and let everyone know if it works for you.
-- Jon
