parfor - classification problem

I do not understand what the problem is in the following code:

 % ...everything is defined in a way that a usual 'for' works fine
    parfor l = 1:length(y)    
        for k = 1:length(z)        
            r = [0 2 3]; %position
            for i = 1:length(R)
                for j = 1:length(d)
                    r0 = [0 0 d(j)];
                    Myfield = B_field_loop(n,r,r0,R(i));
                    B_y(l,k)= B_y(l,k) + Myfield(2);
                    B_z(l,k)= B_z(l,k) + Myfield(3);
                end
            end
        end
    end

the error than I get is :

??? Error: The variable B_y in a parfor cannot be classified.

thanks in advance for every hint!

Answer 1

[Florian]

the order is mixed up for this configuration. using

      for l = 1:length(y)    
          parfor k = 1:length(z)

instead, does the job!