Hi folks.
I get these messages a lot from my ACS 4.0 box. Note the typo: authetication vs authentication. This typo is "in" the ACS messages, and even some Cisco documentation (but doesn't say what the error means)
I think the error is related to wireless PEAP auth.
Message-Type=Authen failed,Authen-Failure-Code=Authetication session invalidated