Ok guys here you go:
Edit the index.php file inside the root of your modx website and paste the following code at line 99:
// Quick IIS friendly url fix - note: this is a quick fix!
$url = $_SERVER[’QUERY_STRING’];
list($err,$url) = explode(";",$url);
if($err==’404’ && !$url) $_GET[’q’]=$url;
This should do the trick for friendly urls using IIS. Next you need to change your custom 404 URL to point to the index.php file. That’s it!
Now point your browser to your new website. For example,
http://www.mymodx.com/home.html
More into on setting up IIS with custom error page redirects
1) Open IIS Manage In MMC.
2) Right Click on the web site node and choose properties.
3) Click on the Custom Errors Tab.
4) Scroll down until you see the HTTP Error -- 404.
5) Double click on 404 to open the "Error Mapping Properties" dialog.
6) Change the Message Type to URL.
7) For the URL enter in /index.php
8) Click OK and Then OK again