I use this plugin on about 100 sites and love it.
Some of these sites were created way back in 2005, 2006 and thus may have differences of some sort. I've kept the WP versions and plugins up-to-date, but never altered the db in any way or touched the wp-config.php file which has had significant changes since the early WP days.
I just upgraded the plugin to the latest version and I got this error -
ERROR: Cannot set DB charset to DB_CHARSET
on 2 websites which I know are quite old. Perhaps it's a db setting somewhere, but the db is no longer backed up. The previous versions of Backwpup worked fine.
It's not that huge of a deal, but thought you should know.