Magento reindex catalog product flat error: Error in foreign key constraint

I have an error when I try to reindex Magento 1.7 catalog product flat index (through admin panel or command line).

On the command line I get the following error:

Product Flat Data index process unknown error:
exception 'PDOException' with message 'SQLSTATE[HY000]: General error: 1005
Can't create table 'databasename.#sql-340a_22a3' (errno: 121)' in
/var/www/clients/client1/web16/web/lib/Zend/Db/Statement/Pdo.php:228

When I look in mysql using 'SHOW ENGINE INNODB STATUS;', I get the following error:

160830 10:17:09 Error in foreign key constraint creation for table
`databasename`.`#sql-340a_2160`.
A foreign key constraint of name 
`databasename`.`FK_MAGE_MAGE_CAT_PRD_FLAT_1_ENTT_ID_MAGE_CAT_PRD_ENTT_ENTT_ID`
already exists. (Note that internally InnoDB adds 'databasename'
in front of the user-defined constraint name.)
Note that InnoDB's FOREIGN KEY system tables store
constraint names as case-insensitive, with the
MySQL standard latin1_swedish_ci collation. If you
create tables or databases whose names differ only in
the character case, then collisions in constraint
names can occur. Workaround: name your constraints
explicitly with unique names.

Any idea how to fix this?

Solution

Disable foreign_key_checks MySQL option before reindex

SET foreign_key_checks = 0;
// job
SET foreign_key_checks = 1;