Hi,
WordPress 2.8.4
It's too old... see on the plugin page: http://wordpress.org/plugins/updraftplus/ - "Requires: 3.2 or higher".
Note that if you can use a sufficiently old version of Simple Backup - not sure which, you'll have to experiment - http://wordpress.org/plugins/simple-backup/developers/ - then backups that it creates can be restored on later WordPress versions by UpdraftPlus Premium. So if your strategy is to upgrade, then that's one option.
Best wishes,
David
