IIS will return the "Forbidden" error when it can't find a default web page to serve and directory browsing is disabled.
A wrong and dangerous solution is to turn on directory browsing as IIS and other helpful articles might suggest.
The most likely problem is that IIS is not fully setup to serve Dotnet webpages and so it can't find the dbFront application.
It might also be that when IIS was installed or upgraded that the entry "default.aspx" was missed or removed from the list of default documents. Please open the entry "Default Document" and view the list to ensure that "default.aspx" is included in the list.
For complete details on setting up IIS please see: Preparing Windows to host a Dotnet 4.0 website