After creating a new CentOS 6.3 VM for a client, we installed Plesk 11.04 and found that all sites running PHP as a FastCGI application were unable to access other sites using fopen(“$url”).
This affected Joomla, WordPress and other modules which also access other sites.
The FIX!
CentOS running with SELinux Enabled was the problem.
After SELinux was disabled and the VM rebooted all was fine!