too many output argument

I am working on control of robot puma560 by using Matlab Simulink which contains 5 Matlab function blocks. when I run a genetic algorithm to tune PD, it says too many output argument. does ga conflict with Matlab function blocks in Simulink or what?

%fitness function
function y=fit2(x)
global kp kv  
kp=x(1);
kv=x(2);
disp([kp kv])
sim('new_sim2qaex')
y= mean(abs(error));

Too many output arguments.

Error in fit2 (line 8)

y= mean(abs(error));

Error in createAnonymousFcn>@(x)fcn(x,FcnArgs{:}) (line 11)

fcn_handle = @(x) fcn(x,FcnArgs{:});

Error in gamultiobjMakeState (line 27)

Score = FitnessFcn(state.Population(1,:));

Error in gamultiobjsolve (line 8)

state = gamultiobjMakeState(GenomeLength,FitnessFcn,ConstrFcn,output.problemtype,options);

Error in gamultiobj (line 274)

[x,fval,exitFlag,output,population,scores] = gamultiobjsolve(FitnessFcn,nvars, ...

Caused by:

Failure in initial fitness function evaluation. GAMULTIOBJ cannot continue.

[Walter Roberson]

global variables act differently in Simulink. You should avoid using them.

[asmaa abdelstar]

How?

Answer 1

[Walter Roberson]

Assign a value to the variable error before calling sim

Otherwise, MATLAB will think you are referring to the function named error(), which does not have any outputs.

[asmaa abdelstar]

i did that already