Try typing in the ip address as opposed to the host name when discovering the node.

Make sure your network setup is ok, do a nslookup from both the oms and the target node. If you use DNS get your network administrator to check the setup.

Make sure the agent is functioning correctly on the target node, check its status, and make sure it and nothing else are using ports 1748 and 1754 (use tnsping).

Bazza