Hi,
I recently converted a web app from .Net 1.1 to a .Net 2.0.  The app worked fine for months as a 1.1 app but after converting to .Net 2.0 I began seeing the following error in my webserver's event log:

Session state has created a session id, but cannot save it because the response was already flushed by the application. 
The error only occurs intermittently and seems to only occur the first time a particular IP address accesses the page.  If I navigate to the page, get the error, close and reopen the browser and navigate back I no longer get the error.  I do not use any Response.Flushes in the entire app and the app's start page is fairly simple with only a couple session variables being created.  I've tried adding Response.Buffer to the start page but this hasn't helped.  
I googled the error and it seems other people are having this problem as well but I have not found any explanation or solution.  If anyone could shed some light I'd greatly appreciate it.
Thanks,
Seth 

eventhandler in Global.asax?  Are you making any calls to Response.Flush?
Session state id is stored in a cookie. This cookie is a header, and  it has to be
written before any content is written to the output stream. if you do a flush, no headers can be written.   Without looking at your code, the fact that you are saying it seems to happen "the first time" only, that's why my comments.

Thanks for responding Peter.
No, I am not making any calls to Response.Flush nor am I using any event handlers in the Global.asax.
I read elsewhere that people have been experiencing alot of problems with session loss in .Net 2.0 due to the app domain recycling constantly even though no changes where being made to the app or it's directory.  However, I've built several web apps from scratch using .Net 2.0 and not had this problem, just the ones I convert from .Net 1.1.  Also, it's difficult to test since I can't reliably reproduce the error.
Googling the error showed that quite a few other people have had the same problem after upgrading a working 1.1 app to 2.0 but I can't find anything on MS's site or elsewhere.
Thanks for your time,
Seth

you lose session state when the application pool is recycled (unless you r using sql server to store your sessions, of course) if that is your problem, and it occurs frequently, then someone missconfigured your webserver as app. pool recycling can be regulated in IIS. i personally think that the error message received sounds like its the app_pool... just a guess, but i'd take a look at the iis settings... try putting the app in a seperate pool for testing, or regulate the recyle settings.
jj
 

Make sure you are not doing a Response.Redirect() inside your Session_Start event handler in global.asax.vb.  Response.Redirect() causes the Session to be flushed.  And in Session_Start, the Session is not in a state that is ready to be flushed.

Hi,
I had no Session_start events or any others, no Response.Redirect and I was experimenting the problem. When I saw this post I realized that the problem is with upgrade because usually you forget to re-compile all the DLLs you made in 1.1 with the 2.0 compiler. So that is what I did and IT WORKED!!!, no more problems!
Hope this helps someone.