From time to time you may come across errors when trying to view your site after uploading a new scripting language based application.
Sometimes you may get a 403 error when you try to visit the site with mention of a Username or Password being incorrect.
Normally this error is caused by the default document that the script is trying to use is not something IIS knows about. For a script like wordpress, this can be remedied by adding Index.php to the list of default documents. It all dependsd
Occassionally, you may encounter a new error when you add the default document (or completely on it’s own). The error you may receive is a 404 error, despite you knowing that the files does exist in the exact location you are attempting to access it from. If this is the case, then it is probably due to a script handler mapping being incorrect.
Content retrieved from: https://support.appliedi.net/kb/a1044/iis-7-status-codes.aspx.