Web API在本地上工作正常，但在服务器上返回501？

Question

我正在使用WebAPI2。这是我的控制器类：

public class ValuesController : ApiController
{     
    [HttpPost]
    public HttpResponseMessage LoginMethod()
    {      
     HttpResponseMessage response = Request.CreateResponse(HttpStatusCode.OK, "This is a simple message");
     return response;
    }
}

我可以从邮递员本地测试此方法，它可以为我提供适当的输出，但在服务器上失败。此方法位于ValuesController内部，我通过这种方式（在本地）调用

http://localhost:49476/api/values/LoginMethod/

，它运行正常。在服务器上，我通过这种方式致电

http://example.com/api/values/LoginMethod/

它给我错误，状态代码为500 internal server error：

 {
  "Message": "An error has occurred.",
  "ExceptionMessage": "Value cannot be null.\r\nParameter name: nameValueCollection",
  "ExceptionType": "System.ArgumentNullException",
  "StackTrace": "   at System.Web.Http.ApiController.<InvokeActionWithExceptionFilters>d__1.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Web.Http.Dispatcher.HttpControllerDispatcher.<SendAsync>d__0.MoveNext()"
 }

这是我的WebAPIConfig文件：

public static void Register(HttpConfiguration config)
{
    config.MapHttpAttributeRoutes();
    config.Routes.MapHttpRoute(
    name: "DefaultApi",
    routeTemplate: "api/{controller}/{action}/{id}",
    defaults: new { id = RouteParameter.Optional }
    );
}

请建议我我做错了什么？任何帮助将非常感激。谢谢。