Another in a long line of very esoteric issues...

If you are migrating a portal repository, possibly from Production back into Dev or vice versa you may run into the following error when running ptlconfig

STEP 1 : Populating Portal seed in OID
Connected.
Creating Lightweight User Accounts and Groups in OID
Portal schema version is: 10.1.2.0.2
Error code : -6502
Error message: ORA-06502: PL/SQL: numeric or value error
ERROR: creating lightweight users and groups in OID ... exiting

PL/SQL procedure successfully completed.

This happens if you have changed the base dn of your OID. For example, you might have had a dn of dc=concept2completion,dc=net
and then decided to change to dot com
dc=concept2completion,dc=com

or possibly you removed a sub-domain
dc=chicago,dc=concept2completion,dc=net
changed to
dc=concept2completion,dc=net

In either case, you will get the error listed above. The problem is that the script secoidd.sql relies on the dn stored in the table wwsub_model$. Below is an extract of secoidd.sql

if l_subscriber_dn is null then
-- The control should never reach here as the subscriber DN
-- should be available in the wwsub_model$ table.

So, if you get into this position, you will need to update the value in the dn column of wwsub_model$.

Seems like such a simple solution. So simple that I have now gone to the process of figuring it out three times.