c# – 保存图像,GDI中发生了一般错误

A generic error occurred in GDI+

我调用img.Save(path,jpegCodec,encoderParams)时的异常;
这里是所有的代码：

private Image img;

    private void button1_Click(object sender,EventArgs e)
    {
        this.img = Image.FromFile(@"path");

        pictureBox1.Image = img;

        if (img.Height < pictureBox1.Height && img.Width < pictureBox1.Width)
        {
            this.pictureBox1.SizeMode = PictureBoxSizeMode.CenterImage;
        }

        Graphics g = Graphics.FromImage(img);

        Font font=new Font("Arial",16);

        SolidBrush brush = new SolidBrush(Color.Black);

        brush.Color = Color.FromArgb(255,255);

        g.DrawString("myName",font,brush,img.Width - 178,img.Height-105);
    }

    private void button2_Click(object sender,EventArgs e)
    {
        Bitmap bitmap = new Bitmap(img);

        saveJpeg(@"path",bitmap,85L);
    }

    private void saveJpeg(string path,Bitmap img,long quality)
    {
        // Encoder parameter for image quality
        EncoderParameter qualityParam =new EncoderParameter(Encoder.Quality,quality);

        // Jpeg image codec
        ImageCodecInfo jpegCodec = getEncoderInfo("image/jpeg");

        if (jpegCodec == null)
            return;

        EncoderParameters encoderParams = new EncoderParameters(1);
        encoderParams.Param[0] = qualityParam;

        //img.Save(path,encoderParams);
        img.Save(path,encoderParams);
    }
    private ImageCodecInfo getEncoderInfo(string mimeType)
    {
        // Get image codecs for all image formats
        ImageCodecInfo[] codecs = ImageCodecInfo.GetImageEncoders();

        // Find the correct image codec
        for (int i = 0; i < codecs.Length; i++)
            if (codecs[i].MimeType == mimeType)
                return codecs[i];
        return null;
    }

你能帮我吗？