This seems to be general .NET issue that sometimes occurs when you are using web farm or cluster. Could you please try to change your web.config file as described at support.aspdotnetstorefront.com/index.php
You could also eventually disable viewstate MAC validation by setting enableViewStateMac property of <page> element to false.
You can put machineKey setting in your web.config. Here is an example:
<machineKey validationKey="AutoGenerate,IsolateApps" decryptionKey="AutoGenerate,IsolateApps" validation="SHA1" />
But you will need to insert your own keys instead of 'AutoGenerate
' setting. Or you can disable viewstate MAC validation by setting enableViewStateMac
property of <page>
element to false. You can find more information at:
and another great article:
As a temporary fix, you can also add the following key to your web.config file:
<add key="CMSUseViewStateUserKey" value="false"/>
This should only be seen as a temporary solution, as it is not recommended to have this key set to false, as having this set to false reduces your site’s security.
If you are using version 6.0, there were some problems in earlier hotfix versions that could cause this if a user’s IP changed during a single session. Updating to the latest hotfix version may resolve this issue.