Update a webapplication on fly without giving any errors.

Question

Hello all,
              How can i update the new pages to push to server without knowing to clients. I get some error messages when the new version is pushed to server if there is any page open in client machine.

Errog msg : "Failed to load viewstate. The control tree into which viewstate is being loaded must match the control tree that was used to save viewstate during the previous request. For example, when adding controls dynamically, the controls added during a post-back"

Thanks
Vishwas