FCP Cannot save changes - Storage location for one or more libraries is no longer available
I've been working on several FCP projects and have the libraries saved on an external drive. When I started working on one of these projects today, as soon as I try to do anything (add, edit or even play the project), I get the error 'Final Cut Pro cannot save changes to "(name of drive)." The storage location for one or more libraries is no longer available. The libraries will be closed so that no work is lost.' I can open and edit the other projects stored on the same external drive without a problem.
After searching for possible fixes, I've tried creating a new library (on my hard drive) and moving the project there - same error. I tried exporting the library as an xml file and importing it to a new library - I receive this error on import
Any ideas?
MacBook Pro 13″, macOS 10.15