The error message is indicating that something at address y.y.y.y has sent a TCP packet that was not encrypted and the crypto policy on your device expects that it should have been encrypted. As a starting point I would suggest that you compare the crypto policy of your device and the crypto policy of y.y.y.y and see if there are differences. You might also check on y.y.y.y and see if there have been any events that might impact its processing of encrypted packets.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...