Hi Irina,
You need to move the current position in the stream to its begin position (instead of the end) and it should be OK:
var memoryStream = new MemoryStream();
nChartControl1.ImageExporter.SaveToStream(memoryStream, new NSize(500, 500), NResolution.ScreenResolution, new NEmfImageFormat());
memoryStream.Seek(0, SeekOrigin.Begin);
var image = Image.FromStream(memoryStream);
Best Regards,
Nevron Support Team