SharePoint - Site URL Inaccessible from the Server

Despite you having set the 'alternate access mapping' e.g. http://domain.com/, and added the domain url into the server's hosts file, accessing the SharePoint site may encounter HTTP 401 authentication error from the server itself. This issue does not happen if you accessed it from outside.

One cause of this behaviour is related to the loopback security check the Windows server is doing. There are two workarounds as described by an article from Microsoft KB and the following are sufficient to make it work great for me.

1. Click Start, click Run, type regedit, and then click OK.
   
   
2. In Registry Editor, locate and then click the following registry key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa
   
   
3. Right-click Lsa, point to New, and then click DWORD Value.
   
   
4. Type DisableLoopbackCheck, and then press ENTER.
   
   
5. Right-click DisableLoopbackCheck, and then click Modify.
   
   
6. In the Value data box, type 1, and then click OK.
   
   
7. Quit Registry Editor, and then restart your computer.