After you do the reinstall, I suggest that you do not copy the Vue6 content to Vue7 folders. Maybe you are overwriting something you shouldn't, I'm not sure. Maybe that's what caused the problems. For example, Vue creates these prv files if they are not present in the objects folder. Maybe Vue7 creates different prv files from Vue6 and when you copied Vue6 prv files, Vue7 didn't create them and tried to use the existing ones, without success. Or some other thing along these lines.

Anyway, you don't need to do this copy. You can just create a new library in Vue7 and point it to the old Vue6 folders. This way, you'll have Vue6 folders intact and Vue7 folders as they originally are supposed to be. There's a slight inconvenience that when you want to load a tree or something you'll have to look in two folders, though.