I had a weird problem on our CI box (IIS6) where the WSDL was generated via HTTP GET but the associated XML schema files were not (IE: https://ci.yada.net/System.svc?xsd=xsd0). When you browsed to the link the browser would return a "general" HTTP error. Erwyn Van Der Meer saved the day with his blog post on how to solve this. Basically the app pool identity needs to have "list folder/read data" permissions on the %SYSTEM%\Temp folder.