SystemC Simulation

Error: (E115) sc_signal<T> cannot have more than one driver: 
 signal `signal_2' (sc_signal)
 first driver `a.main_action1'  (sc_method_process)
 second driver `a.main_action2' (sc_method_process)
In file: <removed by verify.pl>
In process: a.main_action2 @ 500 ps