I recently encountered a situation where users attempting to login to a SharePoint 3.0 site when using the “Sign In” link were recieving an “Internet Explorer cannot display the Web Page” error. The Web Application was configured to allow Anonymous Access and to also use Integrated Windows Authentication.

No errors showed in either the Application or System logs. The IIS Logs displayed a 401 error:
2008-06-20 14:55:01 W3SVC96982807 ServerIP GET /_layouts/Authenticate.aspx Source=%2Fdefault%2Easpx 80 - ClientIP Mozilla/4.0+(BrowserIdentificationString) 401 1 0. Examination of the HTTP traffic with Fiddler showed the same 401.1 error.

Investigation of the Web Site’s properties in IIS showed that HTTP Keep-Alives were disabled — enabling them resolved the problem.

Integrated Windows Authentication (NTLM) requires HTTP Keep-Alives; this is because Microsoft’s NTLM for HTTP authenticates connections, not requests. This means that the HTTP connection must be kept open while the NTLM handshake completes. More technical information can be found here. There is no method that I know of to get around this limitation other than to not use NTLM.

For those of you who don’t already know, I’ve recently taken a job as a Principal Consultant with MSProjectExperts. My new role is essentially the same as it was with BT; I will be providing Project Management and Project-focused consulting services in the areas of implementation, custom development, custom reporting, and training. I am honored by the opportunity to work alongside Gary Chefetz, Dale Howard, and Tony Zink. I’ll have some pretty big footsteps to walk in, but I’m excited for the challenge.

As part of my role with MSProjectExperts, I will be posting to our newly launched group blog, called ProjectServerHelp. For the forseeable future, I will be continuing to post to EPMFAQ and will be maintaining the EPMFAQ Forums.

I look forward to continuing to serve my readers and the EPM community-at-large in this new role. Please contact me using the if you have any questions, and as always, you are welcome to post in the EPMFAQ Blog Posts Forum.

Thank you for reading EPMFAQ!