Unknown error compiling movie - tiny sections export fine - no one bad clip

Question

This week I've been dealing with a huge pain exporting a 6 minute video on my retina macbook pro. The sequence is 720p 24fps (23.976) and contains a mix of 720p & 1080p (scaled) AVCHD footage, a couple of 1080p GoPro shots, some 1080p time-lapse clips (quicktime h.264) and some mp3 files.
Earlier I was having trouble with playback in premiere, but by replacing one bad clip and rendering the rest in small chunks I am now able to play back the sequence with zero issues within premiere.
However, when I go to export the whole movie, or even a significant chunk, either the system starts spinning its wheels partway through export or I get "error compiling movie - unknown error."
The workaround I have found when that happens is to restart premiere (often having to force quit) and then try to export a smaller chunk. (Restarting seems to be necessary after an export has failed). Sometimes the chunks become ridiculously small, but there is no one clip or section that won't export if the clips are small enough. I have also tried cleaning the media cache trashing the preferences, neither of which have changed anything.
Even when I export using the sequence settings of the sequence (which has already been rendered and plays fine within premiere) the problem persists.
My first question is: how can there be an issue exporting a video with identical settings to a sequence that has already been rendered and plays back fine?? Am I wrong in understanding that no conversion is required in that case? Clearly there is something about the process that I don't understand.
My second question is, if no one clip or clips are to blame, are there any likely culprits in my system? Is there perhaps a less time-consuming workaround?
Finally I want to ask: what good does it do to allow users to put different types of media into one timeline if they can never export it?!?!
This is super frustrating, thank you for any help or insight.

Answer 1

So, I ran into this the first time recently. I discovered it when I copied an adjustment layer for quick grading with an RGB Color Corrector and Color Balance effects in it from a rehearsal cut of a short film.The effects worked fine and rendered out without issue. I imported the sequence into my 'final' cut so I could reuse the titles and adjustment layer. I copied the adjustment layer to the new rough cut of the final sequence and ran into this error when I tried to render it, but only after applying the adjustment layer. I found that if I turned off the Color Balance, the sequence rendered fine. I found that if I moved the Color Balance above the RGB Color Corrector, the effect of the RGB effect completely disappeared AND it rendered correctly (both effects turned on) - so reversing the order worked, but effects were weird. I also found that if I added ANY non-GPU accelerated effects to the RGB Color Corrector that I'd get the same compile error (unknown).
I went through and deleted clips until I got to 0 on the timeline, added a new one back on, and it still wouldn't render. So, I created an entirely NEW sequence, copied all video and audio (not adjustment layer) from the original failing rough cut of the final sequence, and pasted it into this new sequence. I also copied the adjustment layer again from the rehearsal cut into this new sequence and it is rendering just fine.
HOURS WASTED DOING THIS! It would be awesome if Adobe actually tested their products before releasing them instead of forcing us to do it for them. My project consisted of about 30-40 different clips and audio, all from the same DSLR (Nikon D810), nothing fancy, two effects in an adjustment layer applied to the entire sequence, and Premiere couldn't handle it. Given this and some of the comments I read while troubleshooting this on this forum, gives me pause in trusting Adobe products for any real work that has a deadline (unless, of course, you build in the required Adobe testing time into your budget).
So, just another data point; something else to try. Create a new sequence, and copy everything from your non-working one to it, and see if this will jump-start Premier. Worked for me. Good luck.