AForge.net调用多个摄像头问题

求各位大侠帮帮忙，我三个都不能同时调用，能帮我看看吗？三个摄像头都没有问题，切换调用都可以显示！三个只能显示其中的两个！
代码：
// 创建第一个摄像头数据源
              private void StartCameras()
        {
            // 创建第一个摄像头数据源
            if (comboBox1.Enabled == true)
            {
                VideoCaptureDevice videoSource1 = new VideoCaptureDevice(videoDevices[this.comboBox1.SelectedIndex].MonikerString);
                videoSource1.DesiredFrameRate = 10;                videoSourcePlayer1.VideoSource = videoSource1;
                videoSourcePlayer1.Start();
            }            // 创建第二个摄像头数据源
            if (comboBox2.Enabled == true)
            {
                //System.Threading.Thread.Sleep(500);                VideoCaptureDevice videoSource2 = new VideoCaptureDevice(videoDevices[this.comboBox2.SelectedIndex].MonikerString);
                videoSource2.DesiredFrameRate = 10;                videoSourcePlayer2.VideoSource = videoSource2;
                videoSourcePlayer2.Start();
            }            //创建第三个摄像头数据源
            if (comboBox3.Enabled == true)
            {
                VideoCaptureDevice videoSource3 = new VideoCaptureDevice(videoDevices[this.comboBox3.SelectedIndex].MonikerString);
                videoSource3.DesiredFrameRate = 10;                videoSourcePlayer3.VideoSource = videoSource3;
                videoSourcePlayer3.Start();
            }    }