fit with a user-defined function in matlab, error: Custom equations must produce an output vector, matrix,

I'm try to make a fit with a user defined function. The result of the function is an element of a matrix. The function is built in a such a way that even if the input is an array the output is still an array, containing the element of the matrix.

When I try to use it or in Curve fit toolbox or directly in a program I obtain the following error message:

Custom equations must produce an output vector, matrix, or array that is the same size and shape as the input data

If I type my function directly at Matlab prompt I obtain the right results, both if I put one input that an array of values.

Just to add some lines:

 Q1(:,:,j) = [cos(Lq1eff*arg(j))        ,  sin(Lq1eff*arg(j))/arg(j)  ,  0                 ,0                   ,0,0;
      -arg(j)*sin(Lq1eff*arg(j))  ,  cos(Lq1eff*arg(j))    ,  0                 ,0                   ,0,0;
        0            ,      0        ,cosh(Lq1eff*arg(j))    ,sinh(Lq1eff*arg(j))/arg(j),0,0;
                0                   ,       0               ,arg(j)*sinh(Lq1eff*arg(j)),cosh(Lq1eff*arg(j))    ,0,0;
                0                   ,       0               ,  0                 ,0                   ,1,0;
                0                   ,       0               ,  0                 ,0                   ,0,1];

This is the matrix, everything is defined and non zero or infinity. The output is for j=1:length(currents) RTransport11(j)=Q1(1,1,j); end

currents is the input array. How can I solve this problem?

Best Regards Alessandro Cianchi