Validation of viewstate MAC failed,in hosting on a web farm

If a web application is hosted by a web farm or cluster, you would experience this exception if you didn't set up the web.config correctly. The solution for resolving this exception is to ensure the configuration specifies the same validation key and validation algorithm in every single web.config in your deployment. AutoGeneration by default cannot be used in a cluster environment. Below is the sample machinekey config entry for your web.config

 
<configuration>
    <appSettings/>
    <connectionStrings/>
    <system.web>
        <machineKey  validationKey='44DB9132AD56D581F6DBFDD8F09EDFD167B75283771DB3241804B0F03602EBACF6349C724FAC64785F60653EC9F9CA20A4D377387A1677704525FE9147CE6AC3' decryptionKey='C77E66D32F8F554C507DDEC6DA2A1A470B5EE195DA584EDD' validation='SHA1'/>
    </system.web>
</configuration>