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="EB0B9F81708C2806EFA80A8BC45114185C93F5A889DB2FAD506AC43EEFFB258257C397BC0E77B75E6270A730ACE3D174C3F8A926966B2005770860ED8C9774DD" decryptionKey="9319DDD5C1B35E795C00EB4570C6FC37607555F9BDDA5BB38A5F8B39C567D611" validation="SHA1" decryption="AES" />
.net1.1
<machineKey validationKey="9A3A853268DB77E01B91666DC5871CFD76EEBD2A45AE7F742AF5091B9DFF21D8A0217DCA07BC5B54CC20CCFC9BE2F126471A775687C06248D7267694F5F6B9EA" decryptionKey="41E5508C04513907B65A00A24D8DBEBE54858A0C58B5AE85" validation="SHA1" />