On my machine the dbconsole didn't start.

The problem was the timezone didn't match the timezone of the machine/host.

$ORACLE_HOME/solaris_DB/sysman/config$ vi emd.properties

agentTZRegion=+02:00

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how to recreate DBConsole & repository:

export ORACLE_UNQNAME = XXX

emca -deconfig dbcontrol db -repos drop

emca -repos create

emca -config dbcontrol dbhttp://www.rocworks.at/wordpress/?p=225