If you started a Rough Cut edit (in Docs/Stringouts mode) and you're trying to export but cannot, the issue most likely you need to complete the edit first.
Rough Cut edits are those that have a narrative arc.
In this edit type, Eddie suggests a story framework composed of 2 or more "beats".
The beats are shown at the top navigation bars as blue dots:
As you can see in the above, the first beat is completed and the next one has not been completed. Thus, you cannot export this story yet.
This user (in this example) would need to complete the 4 beats (4 dots) and then get to the "Final Cut" (the final 5th dot). Then they can export the Final Cut story which comprises of the both beats.
The want to get to the next beat is to type in the prompt box and tell Eddie you're happy with this beat and to move on to the next beat.