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="8827A703B9ACE7560E41635523004C01997E4DF7F7498AB5268124ADF45A12D4B942C7855FC9EB589EB677BDFA7CEC78D937CF8FC57989237C9009D80876ACF3" decryptionKey="9B359FC4A900720B5C33D698F0E228F3A70541308F9E7EF0526FCE4819E15639" validation="SHA1" decryption="AES" />
.net1.1
<machineKey validationKey="6BAFE9CA4091126E1595872EE39588CBB3C753E279EE59558816D5F46EA0B872AEA1ED45007688F8819F478EEEF4C86111F41430457EEABEA784F35C95E38B2A" decryptionKey="627998B269769ED74DE0455320064107B1D51A007E4C5E8F" validation="SHA1" />