Something wrong with the paths configured by your host into the open_basedir directive in the php.ini file. I ask you to fix the issue or remove the restriction.
The number of times I’ve seen people with “easy backups” which either turned out to not be created correctly, or just be impossible to restore, gives me the idea that this promise is a lie.
Remember that backups are only useful if you can restore them. And the only way you know that for sure is by testing it.
I have asked iFastNet to fix the null byte issue.
I hope you can understand that we’re not just going to disable an entire security system because one piece of software that we discourage people from using doesn’t play well with it.
I am working with Joomla since 2003 and know how to restore a website in couple minutes. No need to download all files with FTP as well as mysql database.