You're getting these errors because the tar program is not able to read those files to add them to your backup. It's probably a user permission thing with the way DH places the files in your user space. The backup is working just fine though - it's just telling you it can't read those few fies.
I would suggest changing the backup so that it only backups necessary folders like your domain.com folder and anything else in your home directory you might need. The script in the wiki is set to only backup your web-accessible domain files.
That's the script from the wiki, if you want to add on more folder than just domain.com do it like this:
(I believe that's the right syntax, but I haven't tested it so no promises.)
Hope this helps.
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