Quicktime output failure-“unknown error”

[Alan Stephens]

I updated my demo video in PrPro CC with a 4K timeline and export to QT Pro res & H.264 1080Pin Media Encoder . The H.264 succeeds every time. The Pro Res does not. I tried copying the sequence to a new project, rendering a clip from the project as 1080P then replacing the 4k clip at the beginning. I also tried rendering the entire timeline. Eventually with various similar adjustments and the encode would stop at a different place. I also tried using other codecs and still failed. I get the billy goat and it says “unknown error” I can edit a new project and sequence with the same clips and it will succeed. I finally tried changing the mercury Playback mode from Open GL to software only, and it succeeded. Isn’t Open CL faster?
My MacBook Pro is the latest model with maxed out ram and CPU and AMD display.
Is “MPB engine software only” the best option?

Alan Stephens

Mac Book Pro 2.8, quad i7, 16 GB Ram, AMD Radeon R9 M370X 2048 MB, OS X ElCapitan 10.11.3
Thunderbolt 1 Promise raid drive