Migrating DHCP from Netware to OES - failure

Apologies if this has been covered previously. I have looked across the forums and many TIDS.

We have DHCP running on a Netware 6.5 sp8 server, which is serving 6 vlans across the network. Each vlan sits on its own network switch.
DHCP works and has been for many years.

Looking to move this to an OES server. This particular server is running SLES10/OES 2.

Used the Migration tool to move 1 subnet. Migration worked ok, and I checked the info via iManager and the java console.
However no clients on the subnet can get an IP address.

If I stop the service and reload the netware NLM - all works. So I know the network is ok. The network switches are Extreme Networks and use IP Forwarding command rather than IP-Helper you get on Cisco etc.

I placed a client on the same vlan as the OES server and configured it for DHCP - which worked. So I know the dhcp service is issuing addresses.

Obviously I missed something, but I don't know what it is. Anyone got any ideas??

Thanks