Hi Barry
This happens when you try to use an older version of XDCAM Transfer with a database created by a newer version of the app. Judging from your post, what happened is that at some point over the last couple of years you have installed one of the newer versions of XDCAM Transfer and when you came to point your app at a new cache location you must inadvertently have pointed it at a prior location, and more specifically, at one that contained the preexisting (and newer versioned) database.
Hope it helps
Andy