Unblock (jQuery BlockUI) after file sent to browser through response stream

Question

I have an <asp:button /> that generates a PDF report. I want to use jQuery BlockUI to display a message that says: Generating Report..

Using: Response.BinaryWrite I am then sending the file to the user so it appears as a file download in the browser.

I cannot get $.unblockUI(); to fire. As soon as the file download begins or has completed or is cancelled I want it to dissappear. Currently it never does.. It's as though the page hasn't been re-loaded, I've hit the server but it comes back with the same page.

Things I have tried:

• Setting a variable in JS to true so on document.ready() it will call a function if set to true. This doesn't work because even though I change the variable in code it doesn't change the HTML that is sent to the client.
• This sort of thing: Sys.WebForms.PageRequestManager.getInstance().add_pageLoaded(function() { $.unblockUI; }); //register with Microsoft way $(document).ajaxStop($.unblockUI); //double the insurance and register with jquery way never gets called..

Can this be achieved with an updatepanel?

Any thoughts?

Also in case it helps:

Response.AddHeader("Content-Disposition", "attachment;filename=""" & ShortFilename & """")
        Response.AddHeader("Content-Length", byteArray.Length)
        Response.BinaryWrite(byteArray)
        Response.Flush()
        Response.End()

I can see why this doesn't work sort of, the page is not refreshing in anyway there's just a response stream being sent to the browser, but surely there's an event I can latch on to?