One of our developers is getting this error randomly when perusing through his local development instance in Sitecore 8.1 Update 3 using Chrome. I am not getting the exception at all on my machine on any of the browsers. Is there an known issue with Chrome on certain machines and what may be the cause of this. Seems when he closes browser or shuts down system it seems to alleviate problem.
If this is really only happening in Chrome, I would suspect an extension. Something must be messing with either the CSRF cookie value or the CSRF hidden form field value. Try it in an incognito window or with extensions disabled. If the problem goes away, find the bad module via process of elimination.
If this can be reproduced in other browsers (most likely by restarting the app pool while using the Sitecore client), then it is likely due to a lack of access to the HKEY_CURRENT_USER registry. This is where ASP.NET stores the auto-generated machine key. If it can't store the key, then it will regenerate it each time the app pool restarts and the app won't be able to decrypt token in the hidden CSRF field.
Theoretically, you shouldn't see this machine key issue in recent versions of Windows unless you are running the app pool under a custom user account. On a developer machine, you should just go with Network Service and set Load User Profile to true. Otherwise, you could set a static machine key in the web.config file.
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