Non existent user error on restore

I'm using Postgresql 7.4.2 on RedHat 9. We backup a database weekly with
the following command:

pg_dump --clean --create --verbose --format=c \
--compress 9 -U admin $DBSID \
| dbdumpsplit $DBSID.dump

where $DBSID is the database name. The database is very large, so we
split the dump in 1GB chunks.

Created a new database to hold a copy of the backup. Then issued
cat $DBSID.dump* | pg_restore -d NEW_DB
This errs with following message:
pg_restore: [archiver (db)] could not execute query: ERROR: user "100"
does not exist

Issuing a \du does not list a user with name or id 100 on the backed-up
database. Created a user with:
createuser -i 100 dropme
Run the restore again, but gave same error!

Tried to drop the user:
dropuser dropme
and it returned an error saying that user dropme owned a database and
could not be dropped.

Please help me cause I'm really baffled with this odd behavior.

--
Werner Bohl <wbohl(at)deepdata(dot)com>
Infutor de Costa Rica