Satyajit-
I disabled the Gallery and got further (i.e. I got the options page where I could choose what user/resource data to backup), but still get this error (with Developer Debugging turned on) when trying to run the backup:
Fatal error: require_once(): Failed opening required '' (include_path='/srv/www/htdocs/moodle/lib/pear:.:/usr/share/php5:/usr/share/php5/PEAR') in /srv/www/htdocs/moodle/mod/gallery/lib.php on line 528