ASP.NET 2.0: Validation of viewstate MAC failed

 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.


Solution:

Add this key to every page of the solution (enableViewStateMac="False")

Example: 
<%@ Page Language="vb" AutoEventWireup="false" Codebehind="Text.aspx.vb" Inherits="TestAssembly.TestPage" enableViewStateMac="False" %>