Just to let you know that I signed out and in again as you recommended and it worked like a charm. (don't you hate it when people ask for advice and don't tell you how it turned out?)
Quite fast and painless really and it's left my firmware and patches alone too.
I don't use any of the measuring facilities or get books over the air on the Forma, just read ones I put on from Calibre so haven't lost anything that I can see.
And Calibre works normally with it now.
Thanks again