Cause: The user or role altered to
IDENTIFIED GLOBALLY has external roles directly granted - these must be
revoked, since external roles cannot be granted to global users or
roles.
Action: Use REVOKE to revoke the
external roles from the user or role to be ALTERed.

Relared Errors:
ORA-28025:
missing or null external name
ORA-28026: user
with same external name already exists
ORA-28027:
privileged database links may be used by global users
ORA-28028:
could not authenticate remote server
ORA-28029:
could not authorize remote server for user string
ORA-28030:
Server encountered problems accessing LDAP directory service
ORA-28031:
maximum of string enabled roles exceeded
ORA-28035:
Cannot Get Session Key for Authentication
ORA-28037:
Cannot Get Session Key for RACF Authentication
ORA-28038:
disallow O2LOGON