The above document is for a spoke-to-spoke VPN configuration between three PIX devices but you should be only interested in the configuration between PIX1 and PIX2 in the document. I suspect the problem is related with the crypto ACL on the PIX?
Let me know if this helps or you need further help - good luck.
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...
[toc:faq]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 and UDP are I...