The reason for this problem could be one of the following.

1. Make sure that OEM and OMS are of the same version. i.e 2.1/2.2

2. The most possible reason could be that you would not be having a repository setted up for the oms. To setup the OEM repository do the following

have a user and a special (you could also use the tools tablespace) created under the database where you would like to create the repository.

$> emca (i.e enterprise manager configuration assistant)

based on the wizerd request, provide the information and create a repository.

Once after creating the repository, make sure that the Intelligent agent and oracle data gatherer are up an running. This one you could check through

lsnrctl dbsnmp_status
vppcntl -status

If they are down, then start them as follows

lsnrctl dbsnmp_start
vppcntl -start

Then start the OMS

oemctrl start oms
oemctrl status oms sysman/oem_temp

Once you confirm that these are all functioning correct,
then you can open the OEM client tool through

oemapp console&

Then discover the node by giving the hostname. Once after you discover the node, go to the preferences and set your email and other preferences, give the usernaem and password for the instances (SYS/SYSTEM) and then the node username should be a valid oracle user name that you would use to login to that host and also provide the password)

Also don't forget to configure your SMPT the email host.

Once you do these, you are ready to create jobs/events and other things

If you have any problems, pl. let us know.

Sam