If in doubt, look at the error message. A quick google tells you what you need to know:
403 error - Google Search
Error 403 Means "Forbidden" - you don't have permission to access some resource on that page, or the page itself.
At a guess, it's in a folder that requires a user to log in with a specific role, but since we don't have any access to your codebase we can't tell.
Compare that page with a working page (probably in a different folder) and compare the web.config files to see if there is any security info in them.