note 48184 added to function.header

I'd been trying to figure out why I couldn't get Internet Explorer to download a file if I used session_start(). It only happened with certain files. Here's the undocumented (I couldn't find anything on it) skinny that I've come up with: If the content type (sent in the Content-type header) is not known to Windows AND the cache-control header contains 'no-store' or 'no-cache' I.E. will error out. I'm using WindowsXP Home and I.E. 6.0. Both 'no-store' and 'no-cache' cause the error by themselves and individually. I've found that always replacing the header with one that excludes those lines works: <? header("Cache-Control: must-revalidate, post-check=0, pre-check=0"); ?> This error would happen when using any PHP function (or anything else for that matter) that may set 'no-store' and/or 'no-cache' in the Cache-control header. Provided the content type is not known to Windows. E.g. <? // this works header("Content-type: text/plain"); header("Cache-Control: no-store, no-cache"); echo($data); // this does not work header("Content-type: foo/bar"); header("Cache-Control: no-store, no-cache"); echo($data); ?> On a side note, content types are kept in the registry under HKEY_CLASSES_ROOT under each file extension. My downloads were failing with zip files sent as application/zip. After adding this content type entry under .zip in the registry, I was able to download the file without a problem. But this was just to test my theory. Changing the cache-control header was the solution. I am unsure how/if this effects I.E. on other platforms. ---- Manual Page -- http://www.php.net/manual/en/function.header.php Edit -- http://master.php.net/manage/user-notes.php?action=edit+48184 Delete -- http://master.php.net/manage/user-notes.php?action=delete+48184&report=yes Reason: bad code -- http://master.php.net/manage/user-notes.php?action=delete+48184&report=yes&reason=bad+code Reason: spam -- http://master.php.net/manage/user-notes.php?action=delete+48184&report=yes&reason=spam Reason: useless example -- http://master.php.net/manage/user-notes.php?action=delete+48184&report=yes&reason=useless+example Reason: contains commercial links -- http://master.php.net/manage/user-notes.php?action=delete+48184&report=yes&reason=contains+commercial+links Reason: useless note -- http://master.php.net/manage/user-notes.php?action=delete+48184&report=yes&reason=useless+note Reject -- http://master.php.net/manage/user-notes.php?action=reject+48184&report=yes Search -- http://master.php.net/manage/user-notes.php