by Ken Task.
If you followed the more info link it shows possible reasons for error.
It does mention "It will also occur during backup if moodle database user has not sql privilege: create temporary tables."
DB user in config.php doesn't have the ability to create temporary tables.
If you have access to the DB via MySQL prompt,
mysql -u SUPERUSER -p
Then issue at the mysql> prompt:
show grants for [DBuserseeninconfig.php]
If you have access to some other MySQL, can't tell you specifically, but
look for something that would indicate privileges a mysql user has.
Must be able to create for backup routine to create temporary tables.
If you are remotely hosted on shared system or some other system that restricts, you might have to contact hosting provider and ask them to grant the DB user in your config.php the ability to create.
Official MySQL docs ref:
http://dev.mysql.com/doc/refman/5.7/en/adding-users.html
'spirit of sharing', Ken