From the error msg, I can see you're trying to add another crypto map (outside_map 40) and bind it to the outside interface. This is not possible as only one (1) crypto map is accepted.
What you do is to add your new VPN peer (ip address) to the existing crypto map 20. For the transform set, you may use different set or same name (if policy is still the same). Example:
crypto map outside_map 20 set peer 188.8.131.52
crypto map outside_map 20 set transform-set ESP-3DES-MD5
For isakmp policy, you may the same or different priority no, e.g isakmp policy 40 ...., with different encryption, hash, group & lifetime value. You need to maintain the authentication method using pre-share, except for different key between peers.
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...