预检的响应具有无效的HTTP状态代码500 Angular 2

Question

我正在开发一个应用程序，其中我有一个post请求从服务器获取数据。即使我已经检查了我的CORS插件和参数。使用Postman这个api工作正常，但使用角度2我得到错误。这是我的http请求代码：

    let relatedVideo = this.http.postRequests('pages/relatedVideo.json', {video_id:videoid});
        relatedVideo.subscribe((vdata:any)=>{
        console.log(vdata);
    })

我的其他api正常工作，但这个导致错误。下面我提到了错误返回：

XMLHttpRequest cannot load http://www.example.com/pages/relatedVideo.json. 

Response for preflight has invalid HTTP status code 500
error_handler.js:54 EXCEPTION: You provided 'undefined' where a stream was expected. You can provide an Observable, Promise, Array, or Iterable.
ErrorHandler.handleError @ error_handler.js:54
next @ application_ref.js:359
schedulerFn @ async.js:93
SafeSubscriber.__tryOrUnsub @ Subscriber.js:223
SafeSubscriber.next @ Subscriber.js:172
Subscriber._next @ Subscriber.js:125
Subscriber.next @ Subscriber.js:89
Subject.next @ Subject.js:55
EventEmitter.emit @ async.js:79
NgZone.triggerError @ ng_zone.js:331
onHandleError @ ng_zone.js:292
ZoneDelegate.handleError @ zone.js:246
Zone.runTask @ zone.js:154
ZoneTask.invoke @ zone.js:345
error_handler.js:59 ORIGINAL STACKTRACE:
ErrorHandler.handleError @ error_handler.js:59
next @ application_ref.js:359
schedulerFn @ async.js:93
SafeSubscriber.__tryOrUnsub @ Subscriber.js:223
SafeSubscriber.next @ Subscriber.js:172
Subscriber._next @ Subscriber.js:125
Subscriber.next @ Subscriber.js:89
Subject.next @ Subject.js:55
EventEmitter.emit @ async.js:79
NgZone.triggerError @ ng_zone.js:331
onHandleError @ ng_zone.js:292
ZoneDelegate.handleError @ zone.js:246
Zone.runTask @ zone.js:154
ZoneTask.invoke @ zone.js:345
error_handler.js:60 TypeError: You provided 'undefined' where a stream was expected. You can provide an Observable, Promise, Array, or Iterable.
    at Object.subscribeToResult (subscribeToResult.js:73)
    at CatchSubscriber.error (catch.js:61)
    at MapSubscriber.Subscriber._error (Subscriber.js:128)
    at MapSubscriber.Subscriber.error (Subscriber.js:102)
    at XMLHttpRequest.onError (xhr_backend.js:95)
    at ZoneDelegate.invokeTask (zone.js:275)
    at Object.onInvokeTask (ng_zone.js:262)
    at ZoneDelegate.invokeTask (zone.js:274)
    at Zone.runTask (zone.js:151)
    at XMLHttpRequest.ZoneTask.invoke (zone.js:345)

抱歉我的英文......