I have noticed a power connection issue with the 501's that may be responsible for what you are seeing. Any shifting of the chassis or power cord causes the PIX to reboot - this might be the 'flashing' of the lights that you are seeing.
We have taken to securing the chassis and cord to prevent this issue.
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...