Is this error or not?

Hello,
at first thanks for the plugin, it is a great tool for me.

Then I have one question: I use your plugin for automatic daily backups but sometimes it emails me this error message (see screenshot): http://imgup.cz/images/2016/06/27/backup-error.jpg

When I open the FTP, the backup file is there and everything seems to be OK including the size of the archove file. Is the backup archive complete or not?

Thanks.

https://ww.wp.xz.cn/plugins/backwpup/