Backups not completing

I had been using wpb2db successfully for awhile, but I just realized that I haven’t had a backup complete successfully since May. It looks like it gets partway done, then it just gets stuck. It looks like it’s trying to keep going, but the percentage never increases. I’m not entirely sure what to try to get it un-stuck. I’ve stopped and restarted the backup several times, to no avail. It looks like I have plenty of processing time. What else can I try?

http://wordpress.org/plugins/wordpress-backup-to-dropbox/