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 <machineKey> 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="788034819657FC44B64385191C5A1B36FB1F38FAED19DCF48E544F4B8838198549155B7125852E99E25BE574E009D08F55983A32799F23E81D7A116BC278DCD3" decryptionKey="825E5E134BF7B0EA4880A84B4FD0AD173EC2FDF6B78289184D50AE9850D76C49" validation="SHA1" decryption="AES" />
.net1.1
<machineKey validationKey="51E04B6A35FF4E137C8E9909937466BB2B38CDBE0A3B2D272722C420D4D4A75DFF566EFE6CD069BCDC8E5F1C3DA961E9484424B242ECF9C7D12B51637A4C8F35" decryptionKey="357DCA553CD01665903F6949B1E61B56A7E54263A23B69F3" validation="SHA1" />