Are you using the Microsoft Active Directory and NPS?
Since you have checked the user name and password, check if the "PAP" is allowed on the Radius "Network Policy".
If you are testing from the SZ GUI, the authentication protocol used is PAP.
Check the below link and refer the page number 24 for the PAP settings.https://support.ruckuswireless.com/articles/000002109
Check the NPS events to see the exact details about the connection failure.