Hey, This topic is stale, but it is still the number one hit on google for this problem. I had this problem this week, I couldn’t render or export or output to tape through FCP, because I continually hit a “Not Found” or “general error” message whenever I hit a specific spot in the timeline. The trouble spot was always in the same location. When i went through compressor, the export was successful, but there was an audio loop/video error during the trouble spot on the timeline. After doing some research, I tried trashing preferences, disconnecting/reconnecting media, restarting my system and much more; nothing worked.
What finally worked was getting out my back-up drive, and opening the project from the external drive, not the internal that I had been working on. This did the trick. I was able to render, print to tape and export through compressor. This was a pain in the neck and almost cost me a deadline, so I hope this helps a few people out.
The problem was with the render files, i changed the render file location halfway through this project, and thats what screwed me up. If you use your back up drive or media manger, DO NOT USE THE OLD RENDER FILES! RE-RENDER!