Manually drop user sysman:
i. Logon SQLPLUS as user SYS or SYSTEM, and drop the sysman account and mangement objects:
drop user sysman cascade;
drop role MGMT_USER;
drop user MGMT_VIEW cascade;
drop public synonym MGMT_TARGET_BLACKOUTS;
drop public synonym SETEMVIEWUSERCONTEXT;

ii. Delete the dbconsole configuration files :
$ORACLE_HOME/ directory
$ORACLE_HOME/oc4j/j2ee/OC4J_DBConsole_ directory

Make sure the _ folder is ALL gone on machine