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="3588AB82AD0DE4D1D8EA1412E0C8BAB87C475F671E9EA5DCFB6DE95CF50AE42F82D379B40C57F71D92F164B291CF6867259ECC5C466514513C7E19663CFC05D5" decryptionKey="663513763C2E93D1138EDEEBC11A9E2BA061728EFEA8AE22077DE97A1D9F87D9" validation="SHA1" decryption="AES" />
.net1.1
<machineKey validationKey="6D9F91DEC4EF5BCB28221DFC07B08504FEB619E657579C63D93ACED75495095821067928B3D08C72A8971EE52A05F0405C32925B7E1726F886BA006ABF9C6320" decryptionKey="690A1D73530ACFCDFE9F4D5F2A43DC439C1BF6A254F80C1D" validation="SHA1" />