Error in SharePoint Designer 2010 with WCF -The server could not complete your request

I have tried to open my web application in SharePoint Designer 2010 but unfortunately i got the following error :

The server could not complete your request.

For more specific information , click the Details button (there are nothing :)) so i have solved this error by open the web.config then go to

<system.serviceModel>

which related to WCF and then remove the below tags .

<behavior>
          <!-- To avoid disclosing metadata information, 
          set the value below to false and remove the metadata endpoint above before deployment -->
          <serviceMetadata httpGetEnabled="True" />
          <!-- To receive exception details in faults for debugging purposes, 
          set the value below to true.  Set to false before deployment 
          to avoid disclosing exception information -->
          <serviceDebug includeExceptionDetailInFaults="True" />
        </behavior>

Done.