Hi Zee,
I seem to have this same problem about once a week.
Sometimes I will try restarting the computer with the external drives off, then turn them on. If this doesn’t work, I will trash the FCP preferences, launch the project and then reset my preferences in FCP.
Re: autosave vault… if you are able to open the project from a previously saved autosave file, be sure and “save your project as” once you open it. Otherwise I have found myself with two projects with the same name.
Hope this helps,
Randy