This tip pertains to all versions of SharePoint and no versions of SharePoint. Again, it is really more of an IIS troubleshooting tip.
Since you have gone through Tip 30 and enabled all of the extended logging options in IIS you will not doubt have access to the “Protocol Status” and “Protocol Substatus” fields in all of your IIS logs. If not, go back and run through the tip and enable the options.
When a user cannot access a resource in SharePoint there can be many reasons for it. To track down the “why” of the failed access request a good place to start are the IIS logs. These logs are available in the location specified in the logging options in the web site properties. By default they are located at %SYSTEMROOT%\system32\Logfiles in IIS6 and c:\inetpub\Logfiles in IIS7.
The following list was taken from; The HTTP status codes in IIS 7.0.
I will get a little more in depth on these status codes as they relate to SharePoint. As there are many links in the chain of SharePoint security, it is best to have a starting point to begin troubleshooting and the HTTP status code will help in finding that starting point.
401.1
401.2
401.3
401.4
401.5
200.0