[ServiceContract]
public interface IService
{
    [OperationContract]
    [WebGet(UriTemplate = "hello/?n={name}")]
    Message SayHello(string name);
}

public Message SayHello(string name) {
   return Message.CreateMessage(MessageVersion.None, "*", "Hello "+name+"!");
}

Failed to map the path '/rest'.

<?xml version="1.0"?>
<configuration>
  <system.web>
    <compilation debug="true" targetFramework="4.0" />
  </system.web>
  <system.serviceModel>
    <behaviors>
      <serviceBehaviors>
        <behavior>
          <serviceMetadata httpGetEnabled="true"/>
          <serviceDebug includeExceptionDetailInFaults="false"/>
        </behavior>
      </serviceBehaviors>
    </behaviors>
    <serviceHostingEnvironment multipleSiteBindingsEnabled="true" />
  </system.serviceModel>
 <system.webServer>
    <modules runAllManagedModulesForAllRequests="true"/>
  </system.webServer>
</configuration>