The Storage location for one or more libraries is no longer available...

Hi, Had this error pop up today for the first time (and I go back a long, long way): "The Storage location for one or more libraries is no longer available. The libraries will be closed so that no work is lost".

I've trawled the forums and have deleted prefs, made sure permissions are set and moved my external video SDD from a hub connection directly to my Mac, and changed cables.

The error occurs when I create new projects within an Event. Then when I re-open Final Cut the projects I just created aren't visible but when I try and create them again I get a message saying they already exist.

I suspect it's something to do with this particular SSD (4TB Crucial) because when I use different external drives, or the Mac HD, Final Cut runs perfectly.

Anyone have ideas as to why this particular drive would be playing up? I've run it through Disk Utility with no errors.

Thanks!