title: IE8 won't download a file with a custom mime/type with UAC enabled
body: <p>I have a .net service running on the local machine (Windows 7 x64, IE8, .net 3.5, C#) that returns a file to the browser in response to a user action. Using firefox or chrome, the file is downloaded properly and our application is launched via a custom mime type and all is well.</p>
  
  <p>However, with IE8, I receive a dialog "unable to download file  from . Unable to open this internet site. The requested site is either unavailable or cannot be found. Try again later".</p>
  
  <p>Using fiddler, I verified that IE does receive the payload from the service. </p>
  
  <p>If I turn off UAC, IE does download the file and launch the associated application.</p>
  
  <p>Turning off UAC is not a viable solution, as our customers will have it enabled. </p>
  
  <p>How can I get IE8 to launch the associated application with UAC enabled?</p>
  
  <p>EDIT:</p>
  
  <p>After reregistering the mime type with a programmatic id as described <a href="http://msdn.microsoft.com/en-us/library/bb776872%28VS.85%29.aspx" rel="nofollow noreferrer">here</a>, I can get IE to open show the "Open or Save" dialog for the SECOND time the link is requested from the address bar. Why doesn't it work the first time? </p>