All ASP.net web applications use two specific parameters: __VIEWSTATE and __EVENTVALIDATION. When the client part of such application communicates with the server side, every produced HTTP request includes these two parameters.
Their values are essentially dynamic. In fact, they are changing for each request within a session. Of course, they are also different for different sessions.
This means that you cannot repeat the recorded requests “as is” to produce a copy of the recorded session.
Initially the values are produced by the server part of the application and transferred to the client inside the body of each response. After receiving the updated values the client should include them as parameters in the next request. […]
