If an application continually prompts for a username and password, the underlying issue may be improperly formatted or old credentials stored in the Windows Credential Manager. 

Clear the credential manager

• First, close all running applications 
• From the Start menu, navigate to Windows Settings

• In the search bar, search for Credential Manager.
• Open the Credential Manager

Click Windows Credentials

 Remove any stored credentials referencing the application you're having trouble with.

Lastly, restart your computer