It is difficult to say what could have caused this issue. But I think the issue could be due to ssh and re-image. Can you try to run model/version/pnstatus/hostname. And try to find out the disk space status on your remote file system.
As per the migration guide, you must first export your CS-MARS-100E's 4.3.6 configuration and data, re-image the unit to 6.0.1 and then import the configuration and data.
Migrating Data from Cisco Security MARS 4.x to 6.0.1:
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...