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Agreed, the message is not entirely logical and informative. We'll look into improving that.
If the message appears consistently (i.e. EVERY time a certain action is performed) in the core, we'd like to know, so we can fix it, but if it is erratic and only happens once in a while, it is perhaps caused by the session expiration time, which also controls the expiration time for the security token.
We've had reports that very large values in the session expiration time can lead to unintended behaviour in the security token validation, so try setting it to a lower value, if it is indeed very large.
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Cusix Software