I created a custom error page using htaccess but it doesn't work on IE?

Question

Am using .htaccess to create custom error pages, but the thing is that, it works on other browsers such as safari, chrome, firefox, opera but not on IE. here's my code, what is it that am missing why won't it work on IE?

      ###################################
      ##
      ## HTACCESS CONTROL MODULE
      ## USED TO REDIRECT/DYNAMICALLY
      ## CONTROL URL's ON A WEBSITE
      ## 
      ##
      ###################################
       Options +FollowSymlinks
       RewriteEngine on
       RewriteRule ^(.*)\.htm$ $1.php [NC]
       # custom error documents

       ErrorDocument 404 /404.php
       ErrorDocument 403 /403.php
       ErrorDocument 500 /500.php

Answer 1

First of all this behavior can be triggered by this IE (IE8 in my case) setting:

Second, this setting will be ignored in case your error page is larger than 512 bytes. I.e., your error page should be larger than 512 bytes if you want it to show up in Internet Explorer.