Validation of viewstate MAC failed

Add this to your web.config file in the system.web section:

<machinekey validationkey="xxx" decryptionkey="xxx" validation="SHA1" decryption="AES" />

Provide your own validation and decryption keys ("xxx" above), which you can get generated from
here.

This fixed the problem for me.

<machinekey validation="SHA1" validationkey="A1B2C3D4E5F6F6E5D4C3B2A1A1B2C3D4E5F6F6E5D4C3B2A1A1B2C3D4E5F6F6E5D4C3B2A1A1B2C3D4E5F6F6E5D4C3B2A1A1B2C3D4E5F6F6E5D4C3B2A1B2C3D4E5" decryption="Auto" decryptionkey="A1B2C3D4E5F6F6E5D4C3B2A1A1B2C3D4E5F6F6E5D4C3B2A1" />

Wrote this code in webconfg..it is working in vs2012 ultimate..

None of the solutions worked for me mentioned above. At last I waisted a lot of time to dig out the issue.

Culprit was cookies. I tried to make the cookie secured which works where SSL is installed. But it will not work where SSL is not installed. So, whenever you want to create cookie and want to make it secure here is the right technique.

Dim responseCookie = New HttpCookie(AntiXsrfTokenKey)
   With responseCookie
     .HttpOnly = True
     .Value = _antiXsrfTokenValue
   End With

   If FormsAuthentication.RequireSSL AndAlso Request.IsSecureConnection Then
      responseCookie.Secure = True
   End If

This fixed the issue "Validation of viewstate MAC failed"

Open Application Pool settings, Change 'Load User Profile' to true. This worked for me.

One thing I have come across that causes this issue has to do with the recycling intervals of the app-pools on the webserver.

I found this by looking at the event information in Eventviewer/Application logs and the "Task Category" called "Web Event". Then for the time period that this event took place I looked to see if there were any recycled events that took place just before that (Eventviewer/System logs and the "Source" called "WAS".

By default an app-pool will recycle every 1740 minutes (29 hours). If this recycle happened while a user is busy on the site and send post back to the server, the server no longer recognizes the session/viewstate and rejects what is being posted back.

To overcome this from our perspective is to set the recycle event to happen at a specific time of the day when we don't expect activity on the site. In our case 3am in the morning.

Hope that helps someone out there.

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
As I found out, there was a

<base ..../>

tag in header part of my master page, that I added in last tie and before publishing. This tag specify a default URL and a default target for all links on a page. This was the main cause of the fault, this time.
I hope that it will help others too.
regards.
Ebrahimi
aebrs@yahoo.com

Refer to the following thread for a discussion about this issue:

http://forums.asp.net/t/955145.aspx[^]

You can fix this by setting the EnableViewStateMAC property to false. Refer to more information about EnableViewStateMAC in the link given below:

http://msdn.microsoft.com/en-us/library/system.web.ui.page.enableviewstatemac.aspx[^]

If none of above solutions work for you check the following solution:

if you use F5 and your session is sticky CHECK STICKY SESSION TIMEOUT. Your app session timeout and F5 sticky session timeout must be same and sticky session timeout must not less than app session timeout.

STICKY SESSION TIMEOUT works for me and I solved MAC FAILED problem.

Kia mettrik fail korne baleko army me job milsokta he

just place the below code inside the configuration tag in web.config file

<system.web>
  <machineKey validationKey="52B3217F9A9F7B8CE24DEFBD3EDF2B698E37B2ADE33257FAD329A242C11579D0EEDDB67F94CCF27143DCA4BBF9667DDAE78EBEDDD9EABB7C7AB874B5EC443954" decryptionKey="8A3AD1DD400FF3A09F3F5CB27C0411D2E8C7792CE523FD7B" validation="SHA1"/>
</system.web>

<pages controlrenderingcompatibilityversion="4.0" enableeventvalidation="false" viewstateencryptionmode="Always">enableViewStateMac="false">