Originally Posted by seabee
I have some doubts as I NEVER put a book on an SD-card (I only temporarily tried to put some fonts there when I tried to references fonts not embedded in ebooks nor inside the PRS-T1) and I still had this problem (so no possible book number conflict in the SQLite databases)
If you were using it during some of the betas, there were a handful of bugs here and there related to the database at that time. There are also bugs in the T1 where it doesn't properly go into data transfer mode depending on how you plug it in and will try to muck with the DB at the same time the PC does.
If this still occurs in the latest version, I do recommend trying to report on it in the Calibre forums.