MySQL InnoDB failed

The InnoDB storage engine failed to start so all tables were created as MyISAM tables with MySQL’s strange behaviour. As a result, all FK constraints were removed and crashed the server thereafter. (Tip: use "show create table xxx" to check the created table schema.) It seems that during installation, MySQL is not able to create innodb temporary file as shown in error logged in the file mysql\data\.err.

101006 14:36:46 InnoDB: Error: unable to create temporary file; errno: 2
101006 14:36:46 [ERROR] Plugin 'InnoDB' init function returned error.
101006 14:36:46 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed.

The reason is that when innodb starts the tmpdir defined in my.ini should have existed.