Windows Mobile 6.5 - L2TP/IPSec VPN to USG20w

Hi! I have an issue that ZyXel could not resolve, I have a ZyXel USG20w at a customer’s site and a handheld device with windows mobile 6.5 which I would like to connect via VPN to it, L2TP/IPSec is setup and working via windows 7 but not with the windows mobile 6.5 device..Level 1 told me it’s an issue with Phase 2 negotiation not being done properly. I called Motorola and Fishbowl Inventory, no one seems to be able to help with the setup. Any suggestions? Thx