I had a machine this week that would quit Final Cut Pro as soon as it opened. I had seen this before and deleting the Final Cut Pro prefs was enough, but this time, no joy. FCP would open, work, but on the next launch it would just fail again, even after removing the preference file.

I really didn't want to have to reinstall it all again, as Final Cut Studio is a massive install. I decided I would clear out what I could and try that. I again removed the preference file. This can be found in ~\Library\Preferences\Final Cut Pro User Data. I then decided to make sure that all the caches and render files were removed. These are found in ~\Documents\Final Cut Pro Documents. In this folder you should find another set of folders that hold, caches, render files for video and audio, along with autosave files. In these folder their will be more folders and these will be named the same as the projects you have saved in the past.

I really should have cleared each of these project folders out in turn to see which one was the problem, but I went for the whole lot in one go and bingo, it all worked again. Projects that have already been rendered will now need rerendering, but at least Final Cut Pro isn't quitting anymore.

Note: ~ means your home directory. This is your logon name folder that appears within the Users folder at the root of your hard drive.