Unable to retrieve WSDL

I am using the sample code for PHP provide on the site. I generated the API key , and used but even then system is not going through. At first it says call to undefined function , but when i digg the code further and display soap fault, it displays Unable to retrieve WSDL flightaware.com/commercial/fligh … /wsdl1.xml.Please guide me how to setup . I have 6 yrs of experience but even then I am not going through this webservice…