From Joomla! Documentation
Failed to create backup destination "%s"
This can be caused by an invalid destination being specified by the item utilising the backup system. Examples of common situations where this might occur could be that the destination specified is either inaccessible, incorrect or unwriteable by the PHP process.
- Ensure that the parent of the location specified in the error message is writeable by the PHP process.
- Specify a different location.
- Fix the location so that it points to the correct place.
- Class: JBackupSQL
- Methods: backup