Set the prefered credentials for the node and instance. For the instance it should be either sys or system. For the node, it should be a valid user name, with correct permissions. Then try creating a simple jobs like
for instance do select * from v$instance; and for the node job, do a directory listing and confirm that you can
successfully do things. Besure that OMS and OEM are of the same version. If they are different then you would have trouble in creating the events or scheduling the jobs.

Sorry,folks for giving an Unix troble shooting for NT.

Sam