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="AD35317FCDBBFA641A356200EC6A562B270C9ACDBE0BF0250991295D40772655DE27498301CFD8CC192E5973E6BF1287E8E8B47475E6C5E6AAAF77CE80D3C54B" decryptionKey="CD5135504C4BA181DF463215DEF2FFF29D0FAB5BA59D3C2C5CC370A7B66D1F50" validation="SHA1" decryption="AES" />
.net1.1
<machineKey validationKey="AABD8E81E3FEF09E2AE2E64013A220CED506C270E59C0FA5667946C54F48A405E1A2C0D8980A3E18254311E5889522139E26A01A1A2D619A7A7E3B171806BC80" decryptionKey="B3C9C2E17B7EC24D84DD29E080EE93D85F0CADC4D41D0F48" validation="SHA1" />