[Mark Morache]"Grrrr... this is frustrating. I tried it again and it got to frame 5109, which is a few seconds from the very end."
Try deleting *all* the project render files, and don't re render it before you export it. Sounds like corrupt render files, or (hopefully not) a corrupted master file. If that works, run disk warrior or at least disk utility and check your drives...
I had the same error. This solved my problem.
I still am not at the root of what happened, but I do know I was having problems with an external disk that had issues as I was importing my files.
Deleting the render files and then exporting allowed me to export and send to compressor for transcoding, both.
Yeah, I appreciate that we can get around the issue by deleting the render files, but honestly, I often work on projects where my export time matters. Exporting goes a whole lot faster when you're dealing with rendered media.
This is why I like to render as I go, whenever I step away for a minute.
Until they get this fixed, best practice for me is to edit, and render so I can see my effects in full res, then when I need to export, I DUPLICATE my project without render files, and EXPORT THAT.
Now I can keep editing my already rendered project without rerendering.
Don't live your life in a secondary storyline.