I do not know how it happened with a customer but a user "XXX" is the owner of a datatabase and it's objects. Under SQLServer instance "secutity" and "Logins" that user "XXX" is a sysadmin but does not have access checked in "databases". This was causing some application programs returning error messages. The MSSQLserver instance->security->logins for that user under Groups show as "dbo" and the user is "Standard type" with "SQLServer authentication. I can not delete this user and recreate as he owns other databases too. I tried to use sp_change_users_login but that did not fix. Is there a way to fix this user account from group "DBO" to group "XXX" which normally is shown for "SQLServer authentication" and "standard" type user?
Hope my explanation of the issue is understandable.