Hi There are many reasons to reset the session data 1.fails of aspnet_wp or w3wp services while you are using Inproc session mode. 2. modification to Bin directory, Web.config , machine.config, global application file . 3.low memory on the server , where the server may dump the old sessions .... and in case you dont appeneds the sessionId while using cookieless sessions,a new session will assigned to the browser . I think in your case you may have made some modifications in web.config Again whenver you are reading data from any varaible that can be null for any reason make sure first check that should not null Is your problem got resolved ?
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