errant workspaces

Hi.

I use a custom workspace. For no reason, PP began to take an age and a day to fire up. The workaround the last time this happened was to revert to the Default Workspace and rebuild. Very annoying but it taught me the lesson to backup the custom workspace with a copy.

So, I switched to the backup - problem solved. PP then crashed, horribly. When I got back in, I found that I could no longer access either the backup or the default workspaces. I get this message -

But not a problem, as the custom workspace is still accessible, but how do I retrieve the default workspace and how do I get rid of the old backup?