BTW I also tried a backup I made in December which I have restored from before when I went from kloxo to kloxo-mr (so I know that one is a good one), and got same error.
Backup for mysql data (by Kloxo) with create sql dump. So, it's a possible problem for huge database.
If you are using myisam engine, you can safety 'backup' with:
cd /tmp
service mysqld stop
zip -r9y kloxo-mysql-bck.zip /var/lib/mysql -x /var/lib/mysql/mysql /var/lib/mysql/kloxo /var/lib/mysql/mysql.sock
service mysqld start
BTW, it's maybe your mysql data corrupt for certain table. Try 'sh /script/mysql-optimize'.