Add Machinekey tag in <system.web>
<machinekey validationkey="D135F64DA0AE0C2BFC074B612BF5F71C1695BBE22BB94F35D59D7F8A13BB750BDB8BBF7F0A50F4CF8D207DD896EC08DB7EA6D469056A4D9A818C4797696F3DAF" decryptionkey="68BA1C9EF6B05C0BD0857C43DB4D1DCA5AD126BF7934777395A47207F11D8EC1" validation="SHA1" decryption="AES" />
You can generate the validation key from following url,
http://aspnetresources.com/tools/machineKey[
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