It's because Windows has trouble with multiple connections to the same network device. If you want to access a share that's private, you'll have to remove the password Windows has associated with the drive first. You can do this a couple of ways. The easiest is to restart Windows after disconnecting all "Mapped Network Drives." The fastest way is to create an elevated command prompt and type (without the quotes) "net use /del *"
type "Y" when it asks if you're sure.
You'll then need to reconnect directly to the private share by typing \mybooklive\sharename in the search box under Start (or Run if you use the old school theme). It should then accept your password.