The issue has been fixed already in the latest version of the Concentrator code, use either v3.5.5 or v3.6.1 and you should not see this problem again. In case you do go ahead and open a TAC case on this. And this issue occured only in some software states and has only been seen in rare cases.
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...