Vapor Blog : wcf .net 3.5 sp1 breaking change 401 authentication errorhttp://msmvps.com/blogs/alvin/archive/tags/wcf+.net+3.5+sp1+breaking+change+401+authentication+error/default.aspxTags: wcf .net 3.5 sp1 breaking change 401 authentication errorenCommunityServer 2008.5 SP2 (Build: 40407.4157).NET 3.5 SP1 Breaking Change to WCFhttp://msmvps.com/blogs/alvin/archive/2008/11/14/net-3-5-sp1-breaking-change-to-wcf.aspxFri, 14 Nov 2008 10:04:00 GMTd67277c4-116b-43f1-b688-e9ef184ea916:1654124vapordan@hotmail.com0I walked into a booby-trap with .NET 3.5 SP1. Here are the details. You receive a 401 authentication error when you upgrade your server running WCF service to .NET 3.5 SP1. The WCF run-time now requires an identity to be passed in on the call. The identity...(<a href="http://msmvps.com/blogs/alvin/archive/2008/11/14/net-3-5-sp1-breaking-change-to-wcf.aspx">read more</a>)<img src="http://msmvps.com/aggbug.aspx?PostID=1654124" width="1" height="1">wcf .net 3.5 sp1 breaking change 401 authentication error