I'm on windows 10 and the PC updated overnight. Which is a regular thing, and this hasn't happened to me before. I always leave PL/SQL Developer open, but the program was closed when windows did an update and restart last night and now I can't access the workset I had open yesterday, I'm getting an error every time I try to open it. This is the error:

Workset "Project Titan" is locked by another instance of PL/SQL Developer!
It cannot be opened.

How do I unlock it? there isn't any instances of PL/SQL open other then the one I'm trying to open it in.

Can you reboot the PC and try again? There should not be any lock in this case.

If the issue persists after a reboot, start the Workset Manager from the File ribbon, click on the "File Explorer" button at the bottom right, go to the subdirectory with the name of your workset, delete the file named "lock", and try to open the workset again.