You might try running the 'fsck' command to check for and fix any file system errors on the flash.
If that doesn't fix it, you can also try the 'format' command to completely re-format the flash. Before trying this, make sure you have backup copies of your config (maybe not an issue in a HA setup) and your software (ASA and ASDM).
If you are still having issues, I would suggest opening a TAC case.
Here are the command references for the commands mentioned above:
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...