Backup Error – Processing

I am trying to us WP Backitup for the first time before upgrading to WP 4.0. I haven’t purchased a plan yet, as I was trying to make sure it was working for me before investing. When I activate the back up, the process stalls here:

Status

Preparing for backup…Done
Backing-up database…Done
Creating backup information file…Done
Backing up plugins, themes, and uploads…
Zipping backup directory…
Cleaning up…

With the following error message:

An unexpected error has occurred: processing

https://ww.wp.xz.cn/plugins/wp-backitup/