Have you tried some maintenance on the unused flash space? I'd have a go at the suggestions here (as applicable).
If that's to no avail, then a fresh download from cisco.com of the ASA software, preferably using a different system than the one you are curently using - both for the download and tftp (or ftp). Since you've said you replaced the CF card, it's looking to be a problem further upstream.
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...