I was previously outputting my project in 720p 59.94p and had no issues, except for lots of dropped frames from renderer, I switched to 29.97p output and my dropped frames are gone now, however, whenever I select External, I get "unsupported video format" nothing else has changed, just the project from 59.94p to 29.97p.

I did switch the format of the external as well as the project format, so project and external SDI output are the same now. Any ideas why I can't get the output to work? Surely 720 29.97 is a fairly common format for outputting.