Today I got some trouble with one of my development machines for SharePoint development. Yesterday Windows Update said, that there are several updates and I startet the installation. One of the updates was Internet Explorer 8 for Windows Server 2008.

Today I started that virtual machine and tried to access a SharePoint site. I got an authentication dialog (oops!), and after 3 times entering username and password I saw a white window in the browser. No SharePoint site. Tried another site, but the same result.

Then i created a new web application not running on port 80. After creating a site collection within this web application an access to that site was possible. I created another web application using the Default Web Site from IIS. The site collection in that web application could also be accessed.

The difference between the good and the bad sites is, that the bad sites are running with a hostheader in IIS.

With my good old friend Google I found a solution. Brian Farnhill has a blog post, where he describes how to add the DisableLoopbackCheck to the registry. These are the steps that worked 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.

After adding this value and a reboot of the virtual machine, everything works fine. Internet Explorer 8 can access SharePoint sites with a hostheader.