IIS 401.5 Error

Had a really weird problem today where I was getting a IIS 401.5 error on a subweb today. The problem shows up as a 401.2 error in the browser, but when you look at the IIS log it’s reported as a 401.5.

I was running through all my usual ways of debugging these types of issues and non of the usual things worked. Asked a collegue for help because I must be missing something obvious. Then I was verbally walking him through the configuration and I mentioned that the problem was only happening on this subweb. Something clicked on both our faces – it’s a subweb so there is more than one web.config in play here. I checked the web.config file and found that it was busted (the root site did not work either – but no one cares). I renamed the web.config file and bang, the site started working again.

Blogging this on the off chance it helps someone and to get it to stick in my own memory for next time.