Validation of viewstate MAC failed

If you receive the following error,

Server Error in Application.

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.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.Web.HttpException: 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.

You need to add a machinekey in webconfig. Do click on the below link to auto generate some random keys for your requirements.
ASP.NET machineKey Generator

The machine key may look like,


Whenever you make use of ViewState, Session, Forms authentication, or other encrypted and/or secured values, ASP.NET uses a set of keys to do the encryption and decryption. Normally, these keys are hidden and automatically generated by ASP.NET every time your application recycles, but there are times when you want to specify a particular, persistent key.

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