Cannot Delete Files From Document Library

The problem:

I needed to delete several files from my document library. I tried to do it using the ribbon. Alas, nothing was deleted. Fiddler brought to my attention that the request was nioved; the ULS log informed me that a new request to the AccessDenied.aspx page was created. I never saw the AccessDenied.aspx page, so the results were not clear at all.

The solution:

I looked at the log again and learned that, when you are deleting the files using the ribbon, the Web request goes to the WCF client.svc web service (http://site_root/_vti_bin/client.svc/ProcessQuery).

My next step was checking the authentication for my Web application. It turned out that for this particular web application, Anonymous Authentication was disabled. When I enabled it back, everything started working.

Lesson learned:  Disabling anonymous authentication can bring some unpredictable effects.