Final Cut Pro error 10004: renderVideoFrame failed

Does it give you a frame number in the message?

This usually is a problem with the media, or maybe a bad render file.

I'd start by deleting all render files, and try again.

If the error still happens, and shows a specific frame number, change the Time Display to Frames (in Preferences->General) and locate the frame where the problem shows. You may have to edit around the problem.

Try deleting the Render files.

Also trim a few frames from the start if the render files deletion does not work.

Al