Executing Enable_Broker command on the database to enabl SQL SErvice Broker for Push SQL Cache dependencies takes looonnng time. Keep executing for hours and hours
ALTER DATABASE DemoDatabase SET ENABLE_BROKER Solution:
Make sure that you are closing all instances of the database on which you are trying to enable broker. Better to disconnect the database server and connect again and then fire above SQL statement. The SET ENABLE_BROKER needs an exclusive lock on the database.
Hope this helps.