I am using freebsd and im trying to upgrade to mysql 4.1

When i run /scripts/mysqlup i get this error

Searching ports for mysql41-client .........................found mysql41-client in /usr/ports/databases/mysql41-client....Done
cd: can't cd to /usr/ports/sysutils/portupgrade
[Updating the pkgdb <format:bdb_btree> in /var/db/pkg ... /var/db/pkg/pkgdb.db: unexpected file type or format -- Invalid argument; rebuild needed] [Rebuilding the pkgdb <format:bdb_btree> in /var/db/pkg ... [Updating the pkgdb <format:bdb_btree> in /var/db/pkg ... /var/db/pkg/pkgdb.db: unexpected file type or format -- Invalid argument; rebuild needed] [Rebuilding the pkgdb <format:bdb_btree> in /var/db/pkg ... /var/db/pkg/pkgdb.db: unexpected file type or format -- Invalid argument: Cannot update the pkgdb!]: Cannot update the pkgdb!]

What causes it?