Router 2600 VPN problem

Hi,

We are using Router 2600 as our gateway Router for Leased Line

External : Public Ip *.*.*.229

Internal IP : Private Ip 192.168.1.1

NAT: *.*.*.227 - *.*.*.228

We use RSA-SIG "SEC-ID" to connect our site at US But suddenly without any changes doen on router

It stops working but when i use Dal up from other ISP it works good.

What can be the reason or i have to do any changes for this VPN?

Is tehre some ports issue or Natting?

Thanks in advance Chetan