I get this:
Fatal error: Call to undefined function:
blocks_get_block_names() in /var/www/vhosts/moodle/backup/backuplib.php on line 564
This is using the latest nightly development version Moodle 1.4 development (2004080300)
(This is on my new server and so is not in production at the moment).
This was a totally new install, fresh clean database, new clean files area, new download of code.
Sean K Beardie