Discovering node incorrectly due to listener configuration

Oracle 9.2.0.5, Windows 2000

Normally, oracle will dynamically register service with the name defined in the parameter service_names. So if you add the same entry inside the listener.ora, it will list the same service twice when you execute "lsnrctl status" command. Sometimes, it's not necessary to add this entry into listener.ora. But recently, when I was trying to discover node from OEM, I could not discover the database
on that node or the discovering process generated some error. The OMS, agent, listener are all running. OHS and Listener can be discovered. I finally found that I didn't list any service in my listener.ora file. After I added that service, the discovering process is fine. I'm not sure if this is the reason or some kind of oracle bug for 9i. Worth a shot!

Note:
When the same thing happened, you may want to check out the dbsnmp.log, nmiconf.log, and Oracle%Oracle_Home%Agent.nohup file inside the directory %Oracle_Home%\network\log.
Always try restarting Agent.