Sorry for the rather silly question, but what constitutes use?
One of my shared folders is an SMB share mounted by another computer on my network, is that problematic when trying to add a new shared folder?
I read in another thread that shared folders are off limits for uses like Docker storage. I was definitely using a shared folder for my docker storage, I'm going to guess that's the root of my problem here. I'll come back to this thread if I get the error again.