I ran into this problem recently and it took a while to figure out. My website worked perfectly locally, but when it was deployed to a server, it came up with a blank screen and an error code of 403.14 (Forbidden).
As it turns out, I was using the API Help module (which, by the way, is a totally awesome tool — if you are creating APIs you need to check it out!!) That tool is looking for an XML documentation file that is created upon build. If you don’t include that file in your publish process, you’ll get this relatively nasty error, and have pretty much no clue why. Simply include this file in your deployment and the error should go away.
Hope this helps!