I just updated the plugin and tried to backup. Although I backed up successfully just the other day (i.e., before running the WP3.3 update) now it failed twice with the following error
The backup failed to initialise: Error happened at: bootstrap.php(1050) mkdir() [function.mkdir]: No such file or directory. Please consult the event log for more information.
(the event log simply repeats the error with no extra info)