No arquivo emagent.trc, aparece a mensagem abaixo, seria por conta do horário de verão isso? Antes estava tudo funcionando, agora e notamos o problema relato.
2011-10-21 17:44:11,809 Thread-1959787440 WARN collector: Error exit. Error message: Instance Health Check initialization failed due to one of the following causes: the owner of the EM agent process is not same as the owner of the Oracle instance processes; the owner of the EM agent process is not part of the dba group; or the database version is not 10g (10.1.0.2) and above.