ae导出jpeg图像时的问题：Not enough memory to create requested bitmap

大家好啊，我按照例子中的代码写了一个从mapcontrol导出jpeg图片的函数，具体代码如下

double lScreenResolution;
                   lScreenResolution = MainaxMapControl.ActiveView.ScreenDisplay.DisplayTransformation.Resolution;

                   ESRI.ArcGIS.Output.IExport pExporter = new ExportJPEGClass() as IExport;
                   pExporter.ExportFileName = exportJPGDialog.FileName;
                   pExporter.Resolution = lScreenResolution;

                   tagRECT deviceRECT;
                   deviceRECT.bottom = 0;
                   deviceRECT.left = 0;
                   deviceRECT.right = 0;
                   deviceRECT.top = 0;
                   MainaxMapControl.ActiveView.ScreenDisplay.DisplayTransformation.set_DeviceFrame(ref deviceRECT);

                   IEnvelope pDriverBounds = new EnvelopeClass();

                   pDriverBounds.PutCoords(deviceRECT.left, deviceRECT.bottom, deviceRECT.right, deviceRECT.top);

                   pExporter.PixelBounds = pDriverBounds;

                   ITrackCancel pCancel = new CancelTrackerClass();
                   MainaxMapControl.ActiveView.Output(pExporter.StartExporting(), (int)lScreenResolution, ref deviceRECT, MainaxMapControl.ActiveView.Extent, pCancel);
                   pExporter.FinishExporting();
                   pExporter.Cleanup();

但执行到红色这句时总出错：Not enough memory to create requested bitmap.即时我不打开任何文件，空白的mapcontrol也是一样的出错。这是怎么回事啊，代码我对照了很多地方都是基本相同的阿