Hi AgentXMan!
I'm very sorry for the trouble. It's the first time I encounter such error.
After some googling, I found that it is not so rare in any Unreal Engine 4 Games (even Fortnite have it for some users!).
I found an article that may solve your issue :Failed to open descriptor file error
In any case I would suggest to wait friday or saturday as I'll push a new build with a lot of fix, tweaks and novelties.
Thx for your interest!