Internet Explorer was not able to open this Internet site. The requested site is either unavailable or cannot be found.
Couple of days back I got a complaint from one of the client who recently changed their deployment for one of the Portal we have been developing and the complaint was "Portal does not work in Internet Explorer." The same old great song.
I looked at the error, users were unable to download files from Portal over secure-HTTP (HTTPS). I tried it couple of times and found that it's not working really. Error was consistent from IE6 to IE8.
We have to fix this and to begin with I just googled-up with the error message I was getting. "Internet Explorer was not able to open this Internet site. The requested site is either unavailable or cannot be found. Please try again later." Thankfully I got decent amount of Google search results and in first 2 or 3 I found a post from Mark Kolich sharing his similar experience with Internet Explorer and digging in more about that bug.
You can read more about this on Mark's post here on his website. But simple enough it was just a one line fix for the PHP guys. Yes, we have to add following line to get rid of the error message.
Simply just remove the Pragma headers from your force-download code and you're done.