Hi,We have a number of ASP.NET applications that together with some classic ASP make up a SQL Server 2005 data driven practice management system. The system has been running at a client of ours on Windows 2003 server for a number of years without any probs. Recently strange things have started to happen. All of the classic stuff is fine. On most of the .NET pages, the initial page load is fine......the data is retrieved and the page is built successfully. When a post back occurs, the browser sits there for a few minutes then comes back with a 401.1. Entering the (correct) user credentials results in another long pause and another 401.1. Hitting F5 on the initial page does not cause a 401 no matter how many times you repeat this.......its only when you post back that the error occurs.We are using integrated authentication on IIS with pretty much default setup.I have used fiddler to check if the HTTP request is being sent correctly.......and it is. I have checked the IIS error logs but get no clues beyond the 401 error.We have tried re-installing IIS and the .NET framework on this particular server. This made no difference, so we moved the application onto another server on the same network......with the same problem occurring.We moved the application and database off the network altogether and tried it back at our office......and it worked fine with no 401's!Everything is pointing to a network security/setup issue.....we are just not sure where to start on debugging this further. Its as though IIS is losing the identity of the user between page loads when posting back.The IT manager assures us that nothing of any note has been changed on their network recently.Any advice greatly appreciated!!Many thanks in advance

Hi, As this issue is related to IIS, I suggest discussing it in our IIS forum: http://forums.iis.net/ Tim Quan - MSFT