Found my problem, was SE-Linux
Just for info this was Plesk 7.5.4 and the OS is Fedora Core 3. The problem I found was that the SE-Linux (config-system-securitylevel) was set to deny the use of httpd interactivly. When I turned off this setting it worked! Also I found I had to change the mysql seting in the same place for the PHP-MySQL to work in the Plesk Admin.
It is Ironic that things that are meant to make us safer, sometime make important things stop working.