When a domain is running within it's own Application Pool (Windows 2003 IIS6) which has it's own identity CGI scripts such as Perl or PHP fail to execute. The usual error message is

HTTP Error 403 - Forbidden: Access is denied

Each Application Pool identity should be a member of the IIS_WPG to ensure the site has adequate permissions to run. However by default the IIS_WPG is denied the ability to run CGI applications which will cause the application pool to fail when trying to run one of these for that site.

We need to make some adjustments to the servers Local Security Policies.

START > Administrative Tools > Local Security Policy

Select Local Policies > User Rights Assignment

In the list present find Adjust memory quotas for a process right click on this and select properties. Then Add User or Group > Object Types tick the Groups box and then OK the Object Types dialogue. Now in the box Enter the object names to select box type IIS_WPG and then OK this and the other dialogue box.

The same process now needs to be done for Replace a process level token

The IIS_WPG now has the appropriate rights to execute CGI applications. You may need to reboot your server for these settings to take effect.