When the user can't login, either from Windows Client, Mac client or Web portal, the first thing to check is to always go to the web portal and see if the user can login to the web portal.
1. If the user can login to the web portal, now focus on the client, whether it be the Windows, Mac or others.
2. If the user can't login to the web portal, check the error message. Either Auth_Failed or Not_Found.
Auth_Failed: The password is wrong. Make sure you are using correct password. If the user forgets the password, she can reset it from web portal login page.
Not_Found: The user is not in Centrestack. Need to check with the admin to verify the user is already inventoried in the Centrestack.