How to add event listener in SimPowerSystem block?

I am trying to add an event listener in a SimPowerSystem model. Follwoing is the code I wrote in matlab StartFcn

blk = 'IEEE39_EKF_Restart_AVR_EXC_TG_param_estimate2/SS_Subsystemtwo/Subsystem 34/G34';

h = add_exec_event_listener(blk,'PostOutputs',@testing);

Testing function is just to validate the working of listner

function testing( block,eventdata )
disp('Working');
end

However I am getting the following error.

I can assure the path is proper as I ma able to retrieve the parameters of the same block using get_param.

I tried the same thing for a scope block by modifying StartFcn to

blk = 'IEEE39_EKF_Restart_AVR_EXC_TG_param_estimate2/SS_Subsystemtwo/Subsystem 34/Scope';

h = add_exec_event_listener(blk,'PostOutputs',@testing);

It is working properly for the scope block. Kindly help