Drop Enterprise Manager repository manually
Logon SQLPLUS SYS user and follow the following instructions.
EXEC sysman.emd_maintenance.remove_em_dbms_jobs; EXEC sysman.setEMUserContext('',5);
DROP user sysman cascade; DROP role MGMT_USER; DROP user MGMT_VIEW cascade; DROP public synonym MGMT_TARGET_BLACKOUTS; DROP public synonym SETEMVIEWUSERCONTEXT;
Deconfig the dbcontrol
emca -deconfig dbcontrol db -repos drop
Now the new dbcontrol can be created
emca -config dbcontrol db -repos create