If you attempt to upgrade an application through Fantastico and you get the following error message:

The database user_db is not working properly and the creation of a database backup file has failed. Please contact the sysadmin for further assistance. Include this message for reference.

where user_db is the database of the application you are trying to upgrade, you should make sure the permissions of the folder where your application resides are correct.

The easiest way to fix the issue is to change the permissions of the application's folder to 755.