I cannot apply transitions, I keep getting this:An Unknown Error Occurred

Question

When I try to apply a transition, I get this message: +"An Unknown Error Occurred+
+You may be able to continue without any problems. You may also wish to save, quit, and re-launch iMovie HD."+ I did so. Several times. I even saved as a new project. I even shut down and booted from my install disk and ran Disk Utility, repaired permissions and repaired disk. No problems.
When I try to apply a Video FX, like Fast/Slow/Reverse, the clip shows the usual red line underneath but it never completes. It stays red.
Here's my best guess: The common denominator here is a video clip I imported...not from my camera. It was widescreen, or 16:9, or to be specific, 640x272. I wanted it to match the rest of my movie so I used QT Pro to change it to 640x480. Then I used someone's suggestion to drag that into the iMovie's Package Contents Media folder. It worked. That is, when I reopened my iMovie project, that clip played at 4:3 ratio. Beautiful. And that's the only thing I can think of that could be causing this problem.
Any help, please. I am wasting so much time fooling with this.
noodlehead confoun..ddeD

Answer 1

In addition to the above maintenance, you should also delete preferences by closing down iMovie and trashing the file named com.apple.iMovie.plist located in User (the house icon)/Library/Preferences. On relaunch, iMovie will creat a new .plist file to replace the one that you deleted. Often that simple procedure will solve problems like yours.
Additionally, check to make sure that you have sufficient disk space on your start up disk for iMovie to function efficiently. 20GB to 25GB is frequently recommended by users of this forum.
Make sure that your iLife programs are all up to date, particularly Quicktime.
Sometimes 3rd party or Quicktime plugins can conflict with iMovie and cause problems. If you have such plug-ins, temporarily disable them by moving them to a different folder.
You also could try opening your project in a different user and see if perhaps the conflict is specific to your user ID.