Response.TransmitFile not working with Internet Explorer 11

My website works fine with FireFox, and it worked fine with Internet Explorer too up until a few weeks ago (at least).  Now, with Internet Explorer 11 (running on Windows 8 Pro 64 bit), when I click the button to download the file (a Word document), nothing happens.  In FireFox, a dialog is presented asking the user to save or open the file.

What is going on???  I have been having nothing but problems with IE11.  Extremely poor performance all around.

HELP!!!!

Here is the C# code in question:

Response.TransmitFile(filename_goes_here)
Response.Flush();
HttpContext.Current.ApplicationInstance.CompleteRequest();

The three lines above are wrapped in a try/catch, and no exception is thrown.