"This file in use" message using InCopy from DropBox server

Hello, 

We're using InCopy, via dropbox as server, to coordinate a small magazine project where the editors are in the US and our designer is in the EU. He puts InCopy docs on the DB server and we're to access them. I have been able to access one document--a test from a previous issue. But I cannot access any of this issue's articles. We've tried using assignments, and he's tried placing the docs within a folder. (See second screen shot.) I don't have smartsync turned on. And, another employee is able to access the files! So, it is something on my end. (Could it be that I am running Big Sur? My colleague is running Catalina.)

Thank you, 

Lisa

I will check back here often over the next 24 hours.