Solving SAML login error: "A role with SAML permission is required."

If the user has not yet set up the role at all, he could look at the below steps on how to customize a role:

 1. Go to Setup > Users/Roles > Manage Roles > Create a New Role.
Optional: If you just want to customize an existing center role, you can simply go to Setup > Users/Roles > Manage Roles and click on 'Customize'. This is only applicable if the role that you're trying to design is based on an existing NetSuite Standard Role.
 2. Enter a name.
 3. Select the "Center Type". Recommended center type is "Classic Center".
 4. Start selecting the necessary permissions under 'Permissions' tab.
Important: Under Permissions tab > Setup, be sure to select 'SAML Single Sign-on'.
 Optional: If you want that user to have access to the SAML Setup Page from Setup > Integration > SAML Single Sign On, select 'Setup SAML Single Sign-on' as well.
 5. Save the role.
 6. Search the email address that you're using in your SAML test and edit it.
 7. Under 'Access' tab, select the newly created role and click on 'Add'.
 8. Save the 'Employee' record.

Note: If the user has already set up the role and he's still getting the error, he could have selected the permission 'Setup SAML Single Sign-on' instead of 'SAML Single Sign-on'.