If you are receiving a HTTP 401.1 error when browsing to a locally hosted website with a fully qualified domain name (FQDN) or a custom host header and :
- it works locally via IP,
- it works from an external computer via IP,
- it works from an external computer with a FQDN or a custom host header.
Then you should follow Microsoft support article 896861.
If it is a development environment it should be find to just disable to the loopback:
- Click Start, click Run, type regedit, and then click OK.
- In Registry Editor, locate and then click the following registry key:
- Right-click Lsa, point to New, and then click DWORD Value.
- Type DisableLoopbackCheck, and then press ENTER.
- Right-click DisableLoopbackCheck, and then click Modify.
- In the Value data box, type 1, and then click OK.