Okay this one has been doggin me for days.

Started with an AAF imported from Resolve.

It does it as well with other AAF imports.

Its really annoying and makes me want to move to another NLE fast.

Hello Eric,

I had this from a project file from Media Composer where someone else was editing. Everytime I tried to do anything with the new sequence it gave that exact error. I think it's down to a corrupt clip in the timeline? 

Leo

It can be caused by doing any modifications to the sequence while in Resolve and not generating a new AAF.  Or a corrupt clip.  Basically there isn't media where media is expected.