There is a bug in SilverStripe 2.4.4 which breaks open_basedir restriction.
The error usually occurs when you try logging into the CMS.
The bug has been fixed in the development branch of 2.4, and trunk, but you'll need to patch your SilverStripe 2.4.4 working copy if this affects you.
If this affects you, this fix can be applied to resolve the issue: http://open.silverstripe.org/changeset/115314