Help debugging voice calls on 1760

[BeavisLee]

I was able to setup two ethernet attached 1760's to handle calls from one to the other. One unit has 2 FXS ports and the other 2 E&M. I have anolog phones connected to the FXS ports and the E&M ports go to a PBX. Both sides could make and receive calls both from one port on one router to the other port as well as from router to router.
When i took one of the routers to a remote - vpn attached site and made the requsite changes to the ethernet interface address/subnet i get a fast busy when trying to make calls from either end. At the main office, the call rings once at the called extension before it is disconnected. When the main office calls the remote no ring is heard at all, you just get the fast busy. I can still call port to port on the same router.
The firewalls on both ends of the VPN is set to permit all traffic from the routers and nothing is being blocked.
Is there something i am missing? Does the vpn (pptp on isa2004 via dsl) somehow make it impossible to complete the call? The isp swears they are not doing anything unusual.
Beside debug dialpeer which yields criptic messages, is there any other command i can use to see the status of the call and potentially see why it is failing?
Any guidance will be very appreciated.

Kevin

 

[kwing112000]

I am not sure this pertains to you but may be worth looking at. I install Avaya VOIP and whenever we have to go thru Cisco firewalls they have to disable a bunch of the FIX ups in order for it to work. You could try to search the Avaya IP Office thread and someone has asked about the fixups. Maybe it will help.