ipsec nat-transparency not always working ios 12.4(13b)

[9w.boye]

with 2800 (as spokes) and 3745 routers, both having 12.4(13b), ipsec udp-nat-traversal is not always choosen between the vpn-peers. effect: sas are setup but with no traffic going through.

on the hub-site there is a NAT-situation!

curious: only having this problem on one hub site. Any ideas?

[owillins]

This incompatibility applies only when IP addresses are used as a search key to find a preshared key. Modification of the IP source or destination addresses by NAT or reverse NAT results in a mismatch between the IP address and the preshared key.

http://www.cisco.com/en/US/docs/ios/12_2t/12_2t13/feature/guide/ftipsnat.html#wp1035671