Error while authenticating a user

Dear all,

Hope you all are doing well.

Production issue :

When an user tries to login with his username and password. He is getting error message "INTERNAL ERROR OCCURED".

And the standard RFC which i'm using for authenticating user is  SUSR_LOGIN_CHECK_RFC

CALL FUNCTION 'SUSR_LOGIN_CHECK_RFC'

  EXPORTING

       bname                                 = ip_empid

       password                             = ip_password

EXCEPTIONS

       wait                                     = 1

       user_locked                          = 2

       user_not_active                    = 3

       password_expired                 = 4

       wrong_password                   = 5

       no_check_for_this_user         = 6

       password_attempts_limited    = 7

       internal_error                         = 8

OTHERS                                    = 9.

I want to know what is the meaning of this internal error ? something is going wrong with the standard RFC which I am referring to ? Some one please help me out..

Thanks in advance.