Pls help me solve bitmap parameter is not valid exception in ASP.NET

Here is my code:

  public void btnExtract_Click(object sender, System.EventArgs e)
        {
            MemoryStream message = new MemoryStream();
            FileStream key = new FileStream(@"E:\studies\sem8 projects\count.txt", FileMode.Open);
            PaletteUtility util = new PaletteUtility(Server.MapPath(@"~/mini/" + upload.FileName),null);
            util.Extract(message, key);
            message.Seek(0, SeekOrigin.Begin);
            StreamReader reader = new StreamReader(message);
            Label3.Text = reader.ReadToEnd();
            String ch = Label3.Text;
            if (ch == "hello")
                Response.Write("correct image");
            reader.Close();
            key.Close();
        }
    }

    public class PaletteUtility
    {

        public String sourceFileName;
        private String destinationFileName;
        public long CountUseableUnits(Stream keyStream)
        {
            long countUseableUnits = 0;
            long unitIndex = 0;
            byte key;

            Bitmap bmp = new Bitmap(sourceFileName);
            long countUnits = bmp.Width * bmp.Height;
            bmp.Dispose();

            while (true)
            {
                key = GetKey(keyStream);
                if (unitIndex + key < countUnits)
                {
                    unitIndex += key;
                    countUseableUnits++;
                }
                else
                {
                    break;
                }
            }
            keyStream.Seek(0, SeekOrigin.Begin);
            return countUseableUnits;
        }
        public void Hide(int maxPaletteSize, Stream messageStream, Stream keyStream)
        {
            //load the original image
            Bitmap bmp = new Bitmap(sourceFileName);
            ArrayList newPalette = null; //receives the stretched palette
            Hashtable colorIndexToNewIndices = null; //recevies the list of new color indices

            //create a new palette from the existing one
            StretchPalette(bmp.Palette, maxPaletteSize, ref newPalette, ref colorIndexToNewIndices);

            //create a bitmap with the new palette and the hidden message
            Bitmap newBmp = CreateBitmap(bmp, newPalette, colorIndexToNewIndices, messageStream, keyStream);

            //save the new bitmap
            newBmp.Save(destinationFileName);
            newBmp.Dispose();
            bmp.Dispose();
        }
        public void Extract(Stream messageStream, Stream keyStream)
        {
            System.Drawing.Image image;
            image = BitmapFromWeb(@sourceFileName);
            Bitmap bmp = new Bitmap(image);//Here i am getting Parameter is not valid exception
            BitmapData bmpData = bmp.LockBits(new Rectangle(0, 0, bmp.Width, bmp.Height), ImageLockMode.ReadWrite, PixelFormat.Format8bppIndexed);

            //copy all pixels
            byte[] pixels = new byte[bmpData.Stride * bmpData.Height];
            Marshal.Copy(bmpData.Scan0, pixels, 0, pixels.Length);

            Color[] palette = bmp.Palette.Entries;
            byte messageByte = 0, messageBitIndex = 0, pixel = 0;
            int messageLength = 0, pixelIndex = 0;

            //read pixels until the message is complete
            while ((messageLength == 0) || (messageStream.Length < messageLength))
            {
                //locate the next pixel that carries a hidden bit
                pixelIndex += GetKey(keyStream);
                pixel = pixels[pixelIndex];

                if ((palette[pixel].B % 2) == 1)
                {
                    //odd blue-component: message-bit was "1"
                    messageByte += (byte)(1 << messageBitIndex);
                } //else: messageBit was "0", nothing to do

                if (messageBitIndex == 7)
                { //a byte is complete
                    //save and reset messageByte, reset messageBitIndex
                    messageStream.WriteByte(messageByte);
                    messageBitIndex = 0;
                    messageByte = 0;

                    if ((messageLength == 0) && (messageStream.Length == 4))
                    {
                        //message's length has been read
                        messageStream.Seek(0, SeekOrigin.Begin);
                        messageLength = new BinaryReader(messageStream).ReadInt32();
                        messageStream.SetLength(0);
                    }
                }
                else
                {
                    messageBitIndex++; //next bit
                }
            }

            //release the carrier bitmap
            bmp.UnlockBits(bmpData);
            bmp.Dispose();
        }