Routing stopped working

Have 2 servers running 2003 server. server A has Active
directory running DHCP and DNS. Server B is member server
running RRAS configured as a Lan router to connect our
internal network 192.168.4.0 to our Internet gateway
(Sonicwall) 192.168.2.1. All was working well until I
Upgraded the Domain functional level to from Mixed 2000
to Native 2000 try to address a permissions issue (which
it did). Now the computers cannot get on the internet. I
can ping from my workstation(192.168.4.213) to the
sonicwall(192.168.2.1) I cannot ping the sonicwall from
the 2003 router(192.168.4.7 and 192.168.2.6) Are the some
security settings somewhere that could be preventing
this? What exactly does upgrading the Domain functional
level do? Any ideas?