A generic error occurred in GDI+.

protected void txtBrightness_TextChanged(object sender, EventArgs e)
       {
           string filename = Server.MapPath("Sample.jpg");
           string toFilename = Server.MapPath("brightImage.jpg");
           Bitmap bmp = new Bitmap(filename);
           AdjustBrightness(bmp, Convert.ToInt16(txtBrightness.Text), toFilename);
           bmp.Dispose();
           Image1.ImageUrl = "~/brightImage.jpg";
       }

public void AdjustBrightness(Bitmap Image, int Value, string toFileName)
        {
            System.Drawing.Bitmap TempBitmap = Image;
            float FinalValue = (float)Value / 255.0f;
            System.Drawing.Bitmap NewBitmap = new System.Drawing.Bitmap(TempBitmap.Width, TempBitmap.Height);
            System.Drawing.Graphics NewGraphics = System.Drawing.Graphics.FromImage(NewBitmap);
            float[][] FloatColorMatrix ={
                    new float[] {1, 0, 0, 0, 0},
                    new float[] {0, 1, 0, 0, 0},
                    new float[] {0, 0, 1, 0, 0},
                    new float[] {0, 0, 0, 1, 0},
                    new float[] {FinalValue, FinalValue, FinalValue, 1, 1}
                };

            System.Drawing.Imaging.ColorMatrix NewColorMatrix = new System.Drawing.Imaging.ColorMatrix(FloatColorMatrix);
            System.Drawing.Imaging.ImageAttributes Attributes = new System.Drawing.Imaging.ImageAttributes();
            Attributes.SetColorMatrix(NewColorMatrix);
            NewGraphics.DrawImage(TempBitmap, new System.Drawing.Rectangle(0, 0, TempBitmap.Width, TempBitmap.Height), 0, 0, TempBitmap.Width, TempBitmap.Height, System.Drawing.GraphicsUnit.Pixel, Attributes);
            Attributes.Dispose();
            NewGraphics.Dispose();
            NewBitmap.Save(toFileName);
            NewBitmap.Dispose();
        }