The Professional backup software when opened will try to prompt you for the current windows user's login credentials. This is to ensure that even if the machine is sitting at "press ctrl-alt-del" to login that it has access to all the necessary data.
The way to resolve that error would be to enter this information so it can proper impersonate as a user to login:
1. Open the client software application for the user you've created.
2. Click on the [User Profile] button (green pawn icon on lower left) on the applications main window.
3. Insert the password and save.
The Professional software is set to force you to enter this information since it can cause issues if for some reason it cannot authenticate or access the data. This is something we can turn off in your specific branded version of the software so it doesn't try to force it and does not require it. However, this can cause issues on users that do require you to enter this information, and means you will have to be on the lookout and remember to fill it in when users require it.
If you would like to turn off the forcing of impersonation and the requirement for the login details we can but comes with the catch above.
