I have a similar problem but with a twist.....
On connecting my 505 to a new PC (old one crashed terminally), all the books in the reader are tagged for sync, but nothing synchronises with the Library software. If I transfer a book to the Library manually, I get a duplicate appearing in the Reader after a sync.
Could it perhaps be due to the fact that the Reader had these books tagged for sync on my old PC?
Only option seems to be to copy all books to Library and delete manually on the Reader. Any thoughts on how I could do this more quickly?
All comments welcomed; I'm totally flummuxed !