This is incredibly geeky - and only a year or so ago I would never have thought I would be able to do stuff like this.
But after struggling all day with an video editing assignment in Premiere Pro 5.5, wondering why it couldn't recognise any .prproj files after I brought it home and doomed to wait 48 hours to speak to a tech, I eventually ventured forth onto the web, variously trying to streamline a search for answers and lo! - somehow I did.
Or rather, I sort of sussed what was going wrong and then which solution would most likely remedy the problem.
CURSE THOSE PREFERENCE CACHES!
I'm still way behind of course, but I won't be making that mistake again.