Issue Session timeout at 5 minutes or "Validation of viewstate MAC failed" error

[Jude Lobo]

I am getting the above error when my session state goes over 5 minutes, then some posts guided me to go to the IIS application pool and edit the idle timeout value from 5 to 30 minutes, so I did that, but the values cannot be edited. Is there any way of changing the values or some workaround that I can do in the web.config file?
I am using plesk web host edition by the way.

I have attached an image below showing the plesk control panel

 

[IgorG]

Please, try to use Resolution 3d form Case 3 - https://support.microsoft.com/en-us...-state-message-authentication-code-mac-errors

 

[Jude Lobo]

Please, try to use Resolution 3d form Case 3 - https://support.microsoft.com/en-us...-state-message-authentication-code-mac-errors

Do I have to put this setting in my web.config file?

I've looked up an example :

<applicationPools>
<add name="DefaultAppPool">
<processModel identityType="NetworkService" loadUserProfile="true" idleTimeout="00:05:00" />
</add>
</applicationPools>

Is this right?