PHP 5.2.11 (cgi)
PHP is running fine for files operating within IIS's default website. However when a new site is defined with a host header value (such as a subdomain), php doesn't run and IIS returns 502 bad gateway or CGI has misbehaved with an incomplete set of headers error.
The new site is defined exactly the same way as the default site, with the exception that it has it's own application pool and a host header value. What couldbe causing this misconfiguration?