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="3F5A4673EBFAA57E2EBA8FDE90E08895D2A2AD8213DABFDBC5DF17415BE8324A1785F3A39E46DD0E821283AE2A50EEFAE6B5EEEA57C7D09070FFA3E9A7F10CE6" decryptionKey="D0DFF4D5A794934ED97508A38D81010C43F9D28B7F9A7F842353C83DEC4D2E12" validation="SHA1" decryption="AES" />
.net1.1
<machineKey validationKey="80201559EA9A27EEEBEDA050D321A944C9AEB210382FFF9D44348DA86F8AECC544037EA97617B33A67589D364C94EDC5DBD04D41F15604AFE140B33146684ED5" decryptionKey="56C52912FF18C50777669EA835679D1B1E02C6B4F789B224" validation="SHA1" />