problem with grant sysdba to user

Ok, time for some long overdue education. We're starting to move from 8.0.5 to 8.1.7, and looking at OS authentication for the first time.

On the server, Oracle created the group ORACLE_DBA, and placed my domain userid in it when I installed 8.17 (no previous versions of Ora on this machine.) Domain is "xyz" and my userid is PUR003.

Connected as SYSTEM and created user PUR003 IDENTIFIED EXTERNAL. Then did the following:

SQL*Plus: Release 8.1.7.0.0 - Production on Wed Aug 15 10:56:41 2001

(c) Copyright 2000 Oracle Corporation. All rights reserved.

SQL> connect system_at_smstdb
Enter password: ******
Connected.
SQL> grant sysdba to pur003;
grant sysdba to pur003
*

ERROR at line 1:
ORA-01031: insufficient privileges

SQL> connect system_at_smstdb as sysdba
Enter password: ******
Connected.
SQL> grant sysdba to pur003;
grant sysdba to pur003
*

ERROR at line 1:
ORA-01031: insufficient privileges

SQL> connect sys_at_smstdb
Enter password: ******
Connected.
SQL> grant sysdba to pur003;
grant sysdba to pur003
*

ERROR at line 1:
ORA-01031: insufficient privileges

SQL> connect sys_at_smstdb as sysdba
Enter password: ******
Connected.
SQL> grant sysdba to pur003;
grant sysdba to pur003
*

ERROR at line 1:
ORA-01031: insufficient privileges

SQL> So . . . what am I missing here?

--
Ed Stevens
(Opinions expressed do not necessarily represent those of my employer.)