SAP application giving HTTP error 403.2 - Forbidden

You may have seen a screenshot like this a few times in the past.

It's fairly common when you run peripheral services for your business suite on a windows environment. Maybe it's TREX, maybe it's a content server, maybe something entirely third.

And the cause is rather simple: Microsoft supports the use of ASAPI extensions and filters, but prefers that you use modules instead. So the IIS has ASAPI disabled by default. But SAP is "old" technology, so they don't change, just because Microsofts recommendation does. So the trick is to simple enable it.
If you are running server 2008, start the server manager, go to roles, click on the webserver IIS, and in the right hand pane, scroll down to role services. Here you enable ISAPI extensions, and ISAPI filters.
Reboot the server, and notice the difference !

Now, if the difference is you get a permission DENIED instead of forbidden, you may also want to look at if your service user actually has the rights to access files in the virtual directories.