Plotting data using Simulink event listeners

I'm trying to use event listeners to extract data from my simulink model so I can plot it in Matlab. I'm following this guide https://matlabideas.wordpress.com/2011/11/02/guideing-simulink-with-matlab/ but am getting this error.

Error evaluating 'StartFcn' callback of block_diagram 'Practice'. Caused by: Can add listener only when block diagram is executing.

StartFcn is a pushbutton that starts the simulation. It is also the place where listeners are supposed to be attached. Here is the code for pushbutton % --- Executes on button press in start. function start_Callback(hObject, eventdata, handles) % hObject handle to start (see GCBO) % eventdata reserved - to be defined in a future version of MATLAB % handles structure with handles and user data (see GUIDATA)

% open the simulink model
open_system(handles.modelName); 

% Simulink may optimise your model by integrating all your blocks. To
% prevent this, you need to disable the Block Reduction in the Optimisation
% settings.
set_param(handles.modelName,'BlockReduction','off');

% When the model starts, call the localAddEventListener function
set_param(handles.modelName,'StartFcn','localAddEventListener');
%eventhandle = add_exec_event_listener('Practice/Mux', ...
    %'PostOutputs', @localEventListener);

% Start the model
set_param(handles.modelName, 'SimulationCommand', 'start');

global ln1 ln2 ln3 ln4 ln5 ln6 ln7;

h = findobj('Type','axes','Tag','axes1');
cla(h) % Clear axes in case stop, then start is pressed
ln1  = line(0,0,'Color',[1 0 0],'Marker','o','Parent',h);
ln2  = line(0,0,'Color',[0 1 0],'Marker','*','Parent',h);

Here is the code for the listener function eventhandle = localAddEventListener

eventhandle = add_exec_event_listener('Practice/Mux', ...
    'PostOutputs', @localEventListener);

% The function to be called when event is registered.
function localEventListener(block, eventdata)

global ln1 ln2 ln3 ln4 ln5 ln6 ln7;  
% Use this or cell arrays to shorten the code
%eval([char(variable_names{k}) ' = ' num2str(values(k)) ';'],1 )                     
    xData  = get(ln1,'xData'); 
    xData   = [xData  block.CurrentTime];

      yData1  = get(ln1 ,'yData');
      yData2  = get(ln2 ,'yData');
      yData3  = get(ln3 ,'yData');    
      yData4  = get(ln4 ,'yData');    
      yData5  = get(ln5 ,'yData');    
      yData6  = get(ln6 ,'yData');    
      yData7  = get(ln7 ,'yData');        

      % Gets the time and output value
      % Add the latest point to the data    
      yData1   = [yData1  block.OutputPort(1).Data(1)];
      yData2   = [yData2  block.OutputPort(1).Data(2)];
      yData3   = [yData3  block.OutputPort(1).Data(3)];                        
      yData4   = [yData4  block.OutputPort(1).Data(4)];
      yData5   = [yData5  block.OutputPort(1).Data(5)];
      yData6   = [yData6  block.OutputPort(1).Data(6)];
      yData7   = [yData7  block.OutputPort(1).Data(7)];