Thanks for the the suggestions! Yes, it was Quickmail that was causing the problems and thanks to Sakshi for pointing me to the tracker. It looks like the course that it was failing on had two instances of the Quickmail block in the course. I removed one of them and automated backups ran like a champ last night! I changed the code in the Quickmail block to only allow one instance in the course. Thanks for the help!
Backup and restore
Moodle 2.4 backups failing
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