This is the Session Object that i printed out

----This is the one return Nothing
Add
Session timeout: 20
Session Keys has 0
Session Keys:
Session ID is ck4ceayolzj0go55f3w2x1vi
Session cookiesless? False
Session has 0
Session:
Session is Sync False
Session Code Page 65001
Session LCID 1033
Session Mode: InProc
Session CookieMode 1
Session SynRoot HttpSessionStateContainer
Session StaticObjects has 0
Session StaticObjects:
------ This is the one that actually can retrieve object in session
Add
Session timeout: 20
Session Keys has 4
Session Keys:
ProductCategory.FoundNode
ProductCategory.lstNewFileType
ProductCategory.IntLastValueFileFormat
ProductCategory.objPdtCtgr
Session ID is ck4ceayolzj0go55f3w2x1vi
Session cookiesless? False
Session has 4
Session:
TreeNode
List`1
Int32
ProductCategoryInfo
Session is Sync False
Session Code Page 65001
Session LCID 1033
Session Mode: InProc
Session CookieMode 1
Session SynRoot HttpSessionStateContainer
Session StaticObjects has 0
Session StaticObjects:

--- I have been clicking the AddButton for more that 5 times just to came out the one with object instead of nothing ----
Is there any setting I need to do in dnn or server or IIS ----

Thanks in advance

It all most seems like your session is timing out. Do you have a separate App Pool for the site? It may be that the object you are adding is actually null. Can you add one new Set with a hard coded string, then get that in one place and and see if it works.

An app pool is where IIS controls memory and other settings such as time outs. Its a best practice to create a new app pool and assign your application (virtual directory) to that pool. It will prevent cross contamination between applications. Its done in IIS admin. It doesn't sound like this is your problem. Your session settings look very similar to mine. Try using the Application rather then the Session object. Just for kicks and giggles and lets stick with the hard coded strings. Also try adding two new button and in the processing of the first button set a Session key and get it in the second. Again hard coded strings. Check this out: http://www.codeproject.com/KB/aspnet/SessionTimeoutOnDNN.aspx You might want to try posting this to a MS ASP forum if this doesn't work. I'd be interested if you find a solution.