I'm not aware of the iMovie version you are using, but I've copied and pasted below (with a little editing) two possible solutions that I posted recently in other threads regarding iMovie quitting unexpectedly.
Firstly, trashing iMovie's preference file will often fix problems.
Go to your User (Home) folder Library/Preferences (not the Library folder at the top level in Macintosh HD). Similar to Mountain Lion, on Lion (10.7.4), the User Library folder will be hidden (unlike pre-Lion OS X versions). To access it, click on Go in the Finder menu bar, then press and hold down the Option key - the Library folder will appear in the drop down list, enabling access to it.
In the Library/Preferences folder, locate a file named "com.apple.iMovieApp.plist". With iMovie closed, drag this file to the Desktop. When next opened, iMovie will create a fresh preference file with the default settings. If iMovie now runs OK, you can change these settings in the menu item "IMovie>Preferences" if desired. Also, it's now safe to drag the old preference file to the Trash. Trashing the file will not harm your existing Events or Projects.
Secondly, if trashing iMovie's preference file does not fix the problem, you may need to delete one or more third party QuickTime components (as recommended by others in various threads). Some components have been known to cause conflicts with iMovie, particularly if they are older versions that have not been updated to work with current Mac OS X systems.
The component that seems to be causing the most trouble for users is "3ivxVideoCodec.component" (which possibly is associated with installed Flip MinoHD camera software). Two recent iMovie updates (9.0.7 and 9.0.8) did address the issue of incompatible components and should have fixed this. However, have a look in the folder "Macintosh HD/Library/QuickTime" and check if you have the 3ivx component. If so, drag it to the Desktop then see if iMovie opens and works OK.
You may also need to remove other third party components from the QuickTime folder. But don't remove the following two Apple components: "AppleIntermediateCodec.component" and "AppleMPEG2Codec.component".
By a process of elimination, you should be able to isolate the component (or components) that may be causing a problem with iMovie. Remove each one in turn, then try running iMovie. Hopefully you will find the culprit! Trash (or update) any components that are causing problems and drag all others back to the QuickTime folder.
John, your suggestions were very helpful and I appreciate your input. I was not able to keep iMovie up on the desktop more than 20 to 30 seconds before it quit. Once I carried out your first suggestion and got rid of the preference file, I was able to keep iMovie open. I am using iMovie '11, Ver. 9.0.7 (1768).
The now-open iMovie showed my earlier movies in the event library. The minute I clicked on one of them, iMovie shut down, again with the "quit unexpectedly" message. I followed your second suggestion and deleted the "3ivxVideoCodec.component". That didn't help, though, since the program continued to quit whenever I clicked on any item in the event library.
Since I only had a few movies there, which were not too important, I deleted all of them. That helped and I was able to import a new movie into the event library and start to work with it. Once or twice the program quit, but reopened right away and I was able to keep working.
Compared to where I was, your suggestions solved my problem and I thank you. If more problems crop up, I'll post them.
Good to hear that things are now working a little better for you Eyehope. I notice that you are using version 9.0.7 of iMovie '11. As mentioned in my earlier post, another update was recently released - version 9.0.8 - which addressed the problem of incompatible third party QuickTime components (as did 9.0.7, but there must have been other issues that have now been addressed).
So, it would be best if you now update to 9.0.8 - hopefully all your crashing problems will then be resolved!
I had noticed your earlier reference to update 9.0.8 but forgot to do it while working on the other problem. I've done that now. As soon as I tried to open the updated version of iMovie, it alerted me to remove an incompatible item, "lib3ivxEnc.dylib". Once I did that, everything open fine. I've started to work on a new video and everything seems to be going well. I really appreciate all the help.
Great - thanks for letting us know about that problem file. It's good that the 9.0.8 update gives that alert - and that other incompatible files may be causing a problem. So, it's now clear that the 3ivx component file has an associated file that also needs to be deleted. That information will be very helpful for others here having similar problems as you. Thanks again!
I'm having the exact same problem as eyehope except, after I uninstalled iMovie, then reinstalled, then updated to 9.0.8, then remove the com.apple.iMovieApp.plist file...iMovie still doesn't work and does the exact same thing that eyehope described. I would like to try removing the 3ivx files that both John and eyehope described but I can't find them. John said I could find one in MacintoshHD/Library/Quicktime but I can't find the quicktime folder. I tried to find it by opening Finder and clicking on Go in the top menu, then holding options and clicking on Library. Is this the Library location you are referring to where I should be able to find the Quicktime folder?
Please help!!! Thanks!
John said I could find one in MacintoshHD/Library/Quicktime but I can't find the quicktime folder. I tried to find it by opening Finder and clicking on Go in the top menu, then holding options and clicking on Library. Is this the Library location you are referring to where I should be able to find the Quicktime folder?
No, that Library folder (for your User) is where your Preferences folder is located. The QuickTime folder is in the top level Library folder, that is in Macintosh HD (or whatever the name of your Mac is). You don't need to Option-click, just go to Macintosh HD/Library in the Finder and you will see the QuickTime folder in that Library folder.