After applying 10gR2 Patch Set 3 (10.2.0.4) the dbconsole is always configured as secured. If you have problem with https then you must unsecure the dbconsole.
emctl unsecure dbconsole
Warning : Unsecuring the dbconsole does not change the prot number to the unsecure default (5500). It remains as the https port (1158).
https://hostname:1158/em/console -> http://hostname:1158/em/console