Cannot Export Without Unknown Error

I'm trying to export a video for a client and no matter what I try it constantly fails after a couple of minutes.

I'm used to constantly finding work arounds due to random glitches and issues with the adobe suite but this has got me at the end of my tether. I'm working to a deadline and have lost the past four hours trying to find a work around. When it works the software is great but I genuinely spend more time problem solving than I do editing at the moment. I can't exactly tell my client that I can't give them the edit and have no reason as to why..

The exact wording of the error is "Error Compiling Movie. Unknown Error."

I'm running the latest version of Premiere via CC on Mac OS X 10.11.6 on a 12 core Mac Pro. The source footage is a mixture of 1080P and 4K in a 1080P sequence. Something i've done plenty of times in the past and should be no problem.

A few things I have tried so far are different sequence settings, exporting from a fresh sequence, altering the export destination and exporting internally in Premiere as well as using the Media Encoder.

Any pointers would be greatly appreciated!

Thanks in advance!