When setting up a Mac to backup using Time Machine you will get the error invalid username and password. The qnap device does not support encrypted backups and is the reason for the authentication errors.
To get around not being able to setup the time machine you need to type a command in the console on the Mac needing to connect to the qnap device. Once the console is open you need to type this command:
- defaults write com.apple.AppleShareClient afp_cleartext_allow -bool true
Once that is done you should also make sure you have the proper user info. Open the qnap admin interface. You can find the Time Machine section under “BACKUP”, “Time Machine” and the “Time Machine Support” tab.
Hope this saves you a few minutes of banging your head