Webhandler not firing on postback

[:Francis:]

I have a web application that I upload an image to, the image is subsequently saved to the server's temp folder and displayed via a webhandler on the aspx page.

the code for the aspx:

<img src="PreviewImageQualityHandler.ashx" alt="Picture not loaded" runat="server" id="imagePreview" />

The code for uploading the picture and adding a unique id to the Session:

protected void uploadButton_Click(object sender, EventArgs e)
{
	try
	{
		if (FileUploadControl.FileName.EndsWith(".jpg") || FileUploadControl.FileName.EndsWith(".jpeg"))
		{
			string tempFileName = Path.GetTempFileName();
			FileUploadControl.SaveAs(tempFileName);
			Session["tempName"] = tempFileName;
			Response.Write(Session["tempName"]);
			fileName = FileUploadControl.FileName;
		}
		else
		{
			Response.Write("<script>alert('Please select a .jpg/.jpeg image to upload')</script>");
		}
	}
}

The webhandler code:

public class PreviewImageQualityHandler : IHttpHandler, IRequiresSessionState
{   
	public void ProcessRequest(HttpContext context)
	{
		try
		{
			if (context.Session.Count > 0)
			{
				string sessID = context.Session["tempName"].ToString();
				Bitmap bmp = (Bitmap)System.Drawing.Image.FromFile(sessID);
				context.Response.ContentType = "image/jpg";
				MemoryStream ms = new MemoryStream();
				bmp.Save(ms, ImageFormat.Bmp);
				byte[] b = ms.ToArray();
				context.Response.OutputStream.Write(b, 0, b.Length);
			}
		}
		catch(Exception ex) 
		{ 
		
		}
	}

	public bool IsReusable
	{
		get
		{
			return false;
		}
	}
}

My problem is that the webhandler only fires on the first image-upload. If I try and upload a new image, the webhandler never fires.

If I remove everything to do with Session from the webhandler it fires on every single postback, like it should.

If anybody is able to shed some light on my problem, I will be extremely grateful!

Regards

Francis