saved video projects unusable

Hi

Having an infuriating time here… when working with a video project, I open C5, create a new project, import the video and carry on with my work. If I then save and quit (as people do), when I come back to the project I have the video showing up as Invalid or Unsupported, the video window is just black, and I can’t reimport the video, or ANY OTHER format for that matter as they’re all coming up as invalid or unsupported.

Consequently, I have to restart Cubase and start from scratch, create a new project, import the same video (it works perfectly after a restart of Cubase, but only once) and then carry on working until I’m finished and NEVER close the project or the application!

Any ideas? It’s really not on.

I have C5.5.0, am about to try the 5.5.2 update. My Quicktime is up-to-date.