This is the same issue I had when I upgraded to 4.0.5.1710, I ended up having to downgrade to the last version.
It seems to be an issue many have had with the upgrade same issue always nix path.
Here is someone who has the same issue on Can not add new series - #5 by eman31
I downgraded and added the new series, but when upgraded again still can’t add anything new or rename any files currently in my database. Not sure what happened but the update seems to of broken something.
This has caused issues with all my external library and someone suggested to rename the series and move files? I got 4 drives that’s not an easy fix.