Hi folks, I'm creating a set of images dynamically (for a primary navigation), that part is all sweet, however I want to cache the Bitmap objects rather than recreate them each time a page loads. I have the following code:

Cache cache = System.Web.HttpContext.Current.Cache;


			if ( cache[HashImage(_text, _active)] == null )
			{
                                                                 
	               			// Set the width and height
				// Width is calculated by the text length
				Bitmap image = new Bitmap(100, 20, PixelFormat.Format24bppRgb);


				// Set graphic object
				graphic = Graphics.FromImage(image);
				
				Response.ContentType="image/gif";
				

				cache.Insert( "Image1", (Bitmap)image, null, DateTime.MaxValue, TimeSpan.FromSeconds(30));
				

				

				image.Save(Response.OutputStream, ImageFormat.Gif);
				image.Dispose();
			}
			

			else
			{
				Response.ContentType = "image/gif";
				Bitmap image = new Bitmap(cache["Image1"]);
				image.Save(Response.OutputStream, ImageFormat.Gif);
				image.Dispose();
			}

However I get this error: Invalid parameter used. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.ArgumentException: Invalid parameter used. Any ideas?