I might have IF you had enlightened me

As I was thinking; the client is connecting on their 3G via a VPN to their office.
The VPN is setup through the VC network ( am I OK so far ? )
The problem seems to be on the VC side and their implementation of NAT which is interfering with the VPN IP address ( public and private )
The software problem then is on the customer side ( client=mobile / server=office )
What is the software that is giving the problem and what protocols are running ? ( Does this problem occur on all software implementations ? )
Does this occur on a Cisco network / setup ?
The question about what equipment VC is using still stands.