The server URL must include the full endpoint for the service which is being used underneath, so after your URL always add "/services/Soap/u/25.0". The extension is not adding this by default to what comes in from the Site property.
Some more details on the URL structure for accessing SFDC: https://developer.salesforce.com/docs/atlas.en-us.api_asynch.meta/api_asynch/asynch_api_basics_about_uri.htm
Abhi, you can generate a WSDL for your organization and the information will be contained at the bottom of the generated WSDL. You can follow the instructions in this forum post to do that and get your Soap endpoint.