DNxHD render dark

I'm mastering a playout with the Avid DNxHD codec, but whenever I do this, the final playout is much darker than the footage and anyother playout.  Am I missing something in the settings regarding colour space?

The footage was shot and cut at 2K, and the playout is at 1080P.

All other Quicktime etc playouts are fine. It's just the DNxHD.

Any ideas?

Thanks in advance