Connection to VPN Server through a firewall

Hello,

I did establish a VPN connection to our corporate remote network, but i still have a problem.

When i connect through my home dsl connection, it connects without problems

But when i try to connect from office, where the network is protected by a firewall, i stuck in the verification of username/password as if the firewall is blocking some port used by VPN authentication which ends with message error 619

Here is what im talking about:

Tr. Verifying username and password

And here is the topology that im talking about:

I don't know if i have to update my access list in the router to allow VPN response authentication to enter or not..

Thanks in advance!

Regards!

Lotfi BOUCHERIT