>Did you try Fiddler to determine whether (a) or (b) above applies ?

I am not familiar with Fiddler. It looks like a free tool to analyze the round trip of the hit to a server.

>Did you check the IIS event log ?

Are you making reference to the Event Viewer or another log? In the Event Viewer, I do not see anything wrong at this point.

>Is the .axd extension registered on the server ?

If you are talking about Web site\Properties\Home directory\Configuration\Mappings\Application extensions, then yes, .axd is there. It is presently registered to c:\windows\microsoft.net\framework\v4.0.30319\aspnet_isapi.dll with GET,HEAD,POST,DEBUG. If you are referencing something else, I do not know what this means.