Download failed Destination directory for file streaming does not exist

When updating a component (or the core) in wordpress, you may get the error message “Destination directory for file streaming does not exist or is not writable”. This directory is either wp-content/ or a custom path defined in wp-config.php.

To fix this issue, you can remove any define() calls specifying “WP_TEMP_DIR” as key, and enter the following instead:

define('WP_TEMP_DIR', ABSPATH . 'wp-content/');

Also, make sure that there are correct permissions to this folder. In a UNIX environment, this means “755″. In a Windows environment, this means that the IIS Website App Pool Identity should have Modify permissions.

If you have problems detecting which Identity the App Pool is using, you can try adding permissions to the objects “SERVICE ACCOUNT” and “IIS_IUSRS”.