GDI+ 一般请错误(win form)

在修改信息窗体中,pictureBox1的图片是从数据库读出来的,pictureBox1不作任何改动,当点击保存,下面的代码会执行,但会出现"GDI+ 发生一般请错误",那位高手能帮忙解决一下!谢谢!代码:
MemoryStream picStream = new MemoryStream();
byte[] pic = null;
int len = 0;
if(pictureBox1.Image != null)
{
    try
     {
      pictureBox1.Image.Save(picStream,System.Drawing.Imaging.ImageFormat.Jpeg);
      len = (int)picStream.Length;    //这句发生错误
      pic = picStream.ToArray();
      picStream.Close();
      pictureBox1.Image = null;
     }
    catch(Exception ex)
    {
       Error.ErrorMsgBox(ex.Message.ToString());
    }
}