After restoring a database using pg_restore , cannot insert or update records in tables with primary keys

We are using Postgres Version 7.3.2
We backup and restore Postgres databases using pg_dump and pg_restore.
Though pg_restore process does not throw any exception but After using
it for restoring we are not able to insert or update records in the
tables having Primary Keys. The message we get is "The primary key is
not a btree."
When we run postgres in Debug mode then this problem does not come.

The same code of backup restore was working for postgres version 7.2.

Any ideas?

Thanks
Vikas