pg_dump: [tar archiver] could not write to tar member error

Hello!

I'm using PostgreSQL 8.0.2. PG_DUMP can create the backup tar file.
"pg_dump: [tar archiver] could not write to tar member (wrote 2279,
attempted 7211)"
the command I use is: "pg_dump -Ft -Upostgres -b databasename >
/var/tmp/backup.tar"

I've been using postgresql 7.4.2 before and the backup was working properly.
any ideas?

Filip