The underlying connection was closed: The connection was closed unexpectedly in wcf service.

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WCF

1.Failed to invoke the service. Possible causes: The service is offline or inaccessible; the client-side configuration does not match the proxy; the existing proxy is invalid. Refer to the stack trace for more detail. You can try to recover by starting a new proy, restoring to default configuration, or refreshing the service.

Error is : The underlying connection was closed: The connection was closed unexpectedly.

this is my 3 file...

Iservice1.cs

[OperationContract]
        List<Vehicle_Master> GetVehicle();

Service1.svc.cs

public List<Vehicle_Master> GetVehicle()
        {
            //Configuration.ProxyCreationEnabled = false;
            var result = (from var in dcdc.Vehicle_Masters select var).ToList();
            return result.ToList();
        }

Web.config

<configuration>
	
  <connectionstrings>
    <add name="Database1ConnectionString1" connectionstring="Data Source=najar-pc\sqlexpress;Initial Catalog=Database1;Integrated Security=True">
      providerName="System.Data.SqlClient" />
  </add></connectionstrings>
  <system.web>
    <compilation debug="true" targetframework="4.0" />
  </system.web>
  <system.servicemodel>
    <behaviors>
      <servicebehaviors>
        <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="false" />
        </behavior>
      </servicebehaviors>
    </behaviors>
    <servicehostingenvironment multiplesitebindingsenabled="true" />
  </system.servicemodel>
 <system.webserver>
    <modules runallmanagedmodulesforallrequests="true" />
  </system.webserver>
  
</configuration>

I have spend so much time but i have not solve it. please help me..