Internet Explorer Cannot Download https://something

Earlier today, I was asked to troubleshoot a secure site where file downloads were always failing. Having seen this problem many times often over the years, I immediately suspected that the web developer wasn’t aware that

if a user tries to download * a file over a HTTPS connection, any response headers that prevent caching will cause the file download process to fail.

* Note that this applies to “downloaded” files that open in programs other than IE. It does not apply to resources that render inside IE’s HTML rendering engine, like images/script/css/etc.

When Internet Explorer encounters a HTTPS download that will not be cached, the download is aborted with the following dialog box:

Internet Explorer was not able to open this Internet site. The requested site is either unavailable or cannot be found.

The Fiddler web debugger allows you to easily check to see whether a download contains headers that prevent caching.

Cache-preventing headers include:

  • A Cache-Control header with the tokens no-cache, no-store
  • A Vary header that specifies almost anything 
  • A Pragma header that specifies exactly no-cache

Without changing the site’s code, you can easily confirm that the problem is caused by cache-prevention headers using Fiddler’s Filters tab:

Fiddler Filter UI: Remove Cache-Control Header

Fiddler allowed me to determine that today’s instance was caused by cache-preventing headers. After the web developer updates these headers to allow local caching (e.g. Cache-Control: private, max-age=15) the file download process will work correctly.


PS: In the unlikely event that the user has checked the Do not save encrypted pages to disk option inside Tools / Internet Options > Advanced, this error dialog may be shown for any file downloads from secure sites, regardless of caching headers. I recommend that folks avoid enabling this option, and use the Delete Browser History on Exit feature instead.

Update Oct. 2010: I've conducted some further investigation of this issue, and found that (surprisingly) you CAN specify Cache-Control: no-store, no-cache and the download will work, but if you specify these directives in the opposite order, it will fail. Additionally, if you include a Pragma: no-cache header, the secure response will not be cached regardless of other headers. As a comment notes below, the behavior is slightly different for direct navigation (e.g. URL in the address bar) vs. a hyperlink navigation (e.g. user clicks on a link).

Update Feb. 2011: I've modified the file download logic for IE9. IE9 should be able to successfully download a file regardless of HTTPS or Cache-Control headers unless you have the "Do not save encrypted pages to disk" option set.