Have a Small Business Server 2003 server with ISA 2004. Just out of the blue RAS can't get an IP address from DHCP for the internal adapter. The result is, of course, since it doesn't get an IP it can't give any to the clients. No IP's are reserved in DHCP for RAS either. Some address leases do show up with type of DHCP/BOOTP which I have never seen before.
There is a post on this, but no resolution was proided. Microsoft is struggling to come up with the cause.