dtc, to be absolutely safe, I would suggest that you backup your database or Library Server on the client first.
I feel that there is some general confusion about the roles of clients and servers and the terminology doesn't help. I assume that, on your client PC, you have set MC17 in Playing Now and Playing from to use your server's Library Server. As I understand it, when you do this, the client version of MC17 loads the library data from the Library Server on the server PC. This is not held on the client PC in a persistent database. It is loaded each time you start up the client instance of MC17. You could choose to use a different Library Server such as the one on your client PC. As far as I'm aware, MC17 does not synchronise these different Library Servers. It synchronises the client view of the data with the Library Server data. This can be one way - server to client - or both way which requires authentication.
I have multiple Library Servers. Each instance of MC17 is set to synchronise but all of the Libraries remain independent and different.
Backup the Library Server on your client PC then give authentication a try. If it doesn't work as I believe it should, you can restore the library.
Nick.