Generate Machine Key:

If you sick of getting this error:

Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster.

Maybe it is time to specify a machine key... just paste this into your web.config file inside the <system.web> tag.

.net2.0
<machineKey validationKey="576B834369450DB0E75A2575B27BBAA5209FCE61716C96F038C40CF0AFDF8266D010A3BA14A884713320E333EFA8812425E047CCA4A05C7BC53FBDB725CDD144" decryptionKey="210507DEAD0A05E41314777D1782FFF656C07683B3DEE12F76404FFF00067A13" validation="SHA1" decryption="AES" />
.net1.1
<machineKey validationKey="06EC2F96D7B318C3C4BA692D09C3C959CEA31D24514F7F63538BB6FE6EEE12F774415F5F257538C651F8928EA396DA34646B65EEE45FC46F03BD2590757DF63C" decryptionKey="A1C7325FDDABF5E7A6D1818E5B848F595320E55402D2A987" validation="SHA1" />