You may receive multiple prompts for authentication from Outlook clients connected to an SBS 2008 Server at roughly 5 minute intervals. Both local and Outlook Anywhere clients can encounter this issue. OWA clients aren’t affected. To resolve this issue, log on to SBS 2008 Server and install Update Rollup 8 or Rollup 9. To obtain Update Rollup 9 from Microsoft Download Center, see Update Rollup 9 for Exchange Server 2007 Service Pack 1, also available from Microsoft Update and WSUS. As another option, you may log on to SBS 2008 Server and run following command from an elevated command prompt: %windir%\System32\inetsrv\appcmd.exe set config -section:windowsAuthentication /useKernelMode:false. Update from KB 973917 enables authentication at root level of IIS by adding following to C:\Windows\system32\inetsrv\config\applicationhost.config file at a global level: <windowsAuthentication enabled="false" />. After installing Rollup 8 or later or running appcmd specified above, applicationhost.config is modified and previously mentioned entry will look like this: <windowsAuthentication enabled="false" useKernelMode="false">.