Oracle password change using the Verify Password function

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I am trying to write a Change password process to
change user password on an Oracle 8i database with a
Powerbuilder client. When the PL/SQL function supplied
by Oracle (Verify Password) is enabled for the profile
the Alter User username identified by newpassword fails
with a ORA-20003 Verify password has failed.

The function works perfectly from a SQL editor such as
Embarcadero's Rapid SQL.

I found one report that suggests using the OCIPasswordchange()
function but appears to be very involved.