Ran across an interesting problem. While setting up a new Windows 2008 R2 erver and website on IIS; I noticed that the site was generating 500 errors when serving static files (images, css, html, etc.)
I turned on Failed Request Tracing and noticed that I was getting this logged
This configuration section cannot be used at this path. This happens when the section is locked at a parent level. Locking is either by default (overrideModeDefault="Deny"), or set explicitly by a location tag with overrideMode="Deny" or the legacy allowOverride="false".
Based simply on previous experience I went to the IIS Feature Delegation and reviewed the delegation for the various IIS modules.
I found that by setting Handler Mappings to Read/Write the error was resolved.
I'm still not sure why this causes a problem since I'm not defining any custom handlers at the site level.
Perhaps this setting must be read/write even when custom handlers are set at the server level?