IPSec VPN Problem when there are 2 connections same time

Hey guys!

I'm having a problem with a fortigate & remote access VPN configured using the setup wizard.

Everything works well but when there is more than 1 PC trying to connect from the same network (same ISP Router) to the Fortigate remote VPN, the first connection and the 2º connection goes down.

Is there anyway to allow more than 1 connection at the same time, without the need to use a SSL or Site to Site VPN?

Why is this happening? I suppose it's because both users are behind a NAT device, or in other words, PAT... but I can't understand why, as PAT tracks every port association between internal and translated ports.

Thank you very much!