With the latest versions of Promox there is now two repositories. One is set up for paid subscriptions, and one is set up for unpaid subscriptions. Unfortunately by default the paid repository is enabled, so without a valid subscription you can no longer upgrade a server. So to upgrade a server you should do the following:
Now comment out the only line inside this file by putting a # in front of it.
Next you need to add the non enterprise repository:
you should make the file look like this:
deb http://ftp.us.debian.org/debian wheezy main contrib # security updates deb http://security.debian.org/ wheezy/updates main contrib deb http://download.proxmox.com/debian wheezy pve-no-subscription
Now you can update you machine like normal:
apt-get update apt-get -y upgrade apt-get dist-upgrade