The guide from linode seems to be quite incomplete, many required packages and settings are missing.
I recommend to uninstall ispconfig with the uninstall.php script from the ispconfig tar.gz, then redo all steps from the official ispconfig tutorial starting with step 8:
The pure-fpd package from Debian does not work on openvz by default as capabilities in openvz are disbaled. To install it, use this guide form ispconfig faq:
do this right after you finished step 13 of the perfect server guide.