Backup stopped working with weird error message

WP 3.5.1 & BWP 2.3

BWP has stopped working on a large (2+ GB) site. When I visit the backup page, it shows that the backup is running, but it never completes. Sometimes I get an error page that reads:

Page not found.

Followed by lots of white space, then what looks like the menu of my site, for example:

About…

About The Farmer
Our History
Archives and Back Issues
Location and How to Contact Us
Staff
Privacy Policy
Refund Policy

WhereTo Buy
Subscribe
How To…

Buy a Copy
Subscribe
Tell Us What You Think
Report a Change of Address
Submit Photos, Articles or Announcements
Request a Photo
Get a Back Issue
Request Coverage of an Event

(Etc.)

I am also seeing this in .backup_warnings:

{“php”:{“defeb5010a8ffd9371f7f6a6badd5f66″:”Undefined index: post, \/home\/sttamman\/public_html\/wp-content\/themes\/responz\/themify\/themify-config.php, 166″,”281a893ebdfab2b0f2e0ffe9b9446be0″:”Trying to get property of non-object, \/home\/sttamman\/public_html\/wp-content\/themes\/responz\/themify\/themify-config.php, 167”}}

Active plugins installed:

BackUpWordPress
Contact Form 7
Duplicator
Google sitemap plugin
Multiple Galleries
Quick Page/Post Redirect Plugin
Really Simple CAPTCHA
WP Hide Post

Help!

http://wordpress.org/extend/plugins/backupwordpress/