Symptoms
Downloadable files for orders are not being served to customers.
Cause
In IIS 6.0 non-.NET files will not be served by IIS, therefore preventing the download of static files like .pdf's or .zip's.
Solution
You'll need to add to the httphandlers in the web.config file in order to allow the files to be served (see http://support.microsoft.com/?kbid=909641):
<httpHandlers>
<add path="*.pdf" verb="*" type="System.Web.StaticFileHandler" />
</httpHandlers>
If you want the files to be protected with Forms Authentication, you can do the following (may require host assistance):
1 - right-click "My Computer", choose MANAGE.
2 - Drill down: Services and Applications >> Internet Information Services >> Websites.
3 - If you are on a non-server edition of Windows, expand Default Website. Otherwise, skip this step.
4 - Right-click on the application you need to re-map, choose "Properties".
5 - Click the "Configration" button.
6 - On the first tab, you'll see a list of file mappings. Highlight the listing for ASPX, click Edit, and copy the entire entry in the "Executable" box. Make sure you copy the whole path for the DLL.
7 - Click Cancel so you do not mistakenly change any settings.
8 - From the list of mappings, click Add. Paste the executable path in the box, enter the extension in its box(case doesn't matter, but the dot does). Limit verbs to "GET, POST" and uncheck the other two boxes. Click OK a few times and close your way out.
9 - Restart IIS