Unauthorised 401.1 Error received when attempting to connect to site with Security Explorer (4266746)

Security Explorer is installed on a web front-end server and when attempting to connect to a site that is served from the same web front-end server the user credentials are not accepted.

Within Security Explorer if you expand a site or farm in the tasks pane a prompt appears for credentials. When credentials are supplied the prompt returns immediately suggesting that the credentials were ignored or rejected. If the username and password is supplied again the prompt will return again giving the impression that the credentials have been rejected again.

When consulting the IIS or Security Event Logs a "401.1 Unauthorized" error is recorded each time the credentials are supplied.

This issue occurs when the web site you are trying to connect to uses integrated authentication and has a name that is mapped to the local loopback address. This error will only be received if you browse to the web site directly from the hosting server. If accessed from a client machine the web site will work as expected.

There are two methods to resolve this issue. Method 1 is more secure and is recommended for a production environment. Method 2 can be used in a development or testing environment as it is considered less secure.

Method 1: Specify host names (Preferred method if NTLM authentication is desired)

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\MSV1_0

3. Right-click MSV1_0, point to New, and then click Multi-String Value.
4. Type BackConnectionHostNames, and then press ENTER.
5. Right-click BackConnectionHostNames, and then click Modify.
6. In the Value data box, type the host name or the host names for the sites that are on the local computer, and then click OK.
7. Quit Registry Editor, and then restart the IISAdmin service.

Method 1: Disable the loopback check (less secure, less recommended method)

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.