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="BC878629DBE8142F5E7E3F8CAF4E544113112CCE280ED9BBBDBB799EC3237BDDE42B0E7C11BDA49DB17852CB21FEC44848FFE75D2E54417B9487794A28B98FB6" decryptionKey="48CA9D48FC60091BDC97EE868C7AEEB512DB7EC9875CFB14BE509A51BBD89FCA" validation="SHA1" decryption="AES" />
.net1.1
<machineKey validationKey="1E4A1B0581292B4574872169D4E3A2ABFFCC0594AA9E4FCC1ED36AAE24E39065D4351AF7CFA4681037DBB174456CE9A59EF32787A8DC24FE06657D1244C1042F" decryptionKey="5F0F753AFCE361CCD793580CB48CF409DAC874EB8DE7052C" validation="SHA1" />