Unstable IPSEC VPN

[Guest]

[maxxer]

Hi.
I just replaced a customer's ZyWall with EFW 2.5.1, I'm using 2.4 myself.
I had an IPSec vpn configured with Zywall, working fine.
Now that I moved to EFW on the other side as well I thought things would go better, instead I'm having a lot of troubles.
I.e. when I try to downoad "lots" of data, like opening a remote file with vi, the connection drops, screen freezes and won't go further, while if I open a new connection everything is fast and working!

How's possible?
On both sides I used the standard IPsec settings.

any help appreciated!
thanks!