Well, thank Nakamoto (or should that be Larimer) I had a backup.
I don't know what exactly happened. I didn't think it was supposed to overwrite the roaming files. I uninstalled the old client, installed the newer one, and when I ran it, it was as if the old stuff was never there.
As you suggested Riverhead, I needed to replace the json with a copy of the old one!
I shall never update without double checking my backups.
Thanks Riverhead, I will be voting for you (99.57% reliability!)...