Problem with creating multidimensional, multiparameter fit

I've been trying to create a 6-dimensional, 15-parameter fitting function defined in the following way:

func = strcat('(a11*sin(2*pi*x/365.25) + b11*cos(2*pi*x/365.25)',...
'+ a12*sin(4*pi*x/365.25) + b12*cos(4*pi*x/365.25)).*(a21*sin(pi*y/12)',...
'+ b21*cos(pi*y/12) + a22*sin(pi*y/6) + b22*cos(pi*y/6) + a23*sin(pi*y/3)',...
'+ b23*sin(pi*y/3)) + m*w + (a*v.^2 + b*v + c).*u + d');

ft = fittype(func,...
   'independent',{'x','y','w','v','u'},'dependent',{'z'},...
   'coefficients',{'a11','b11','a12','b12','a21','b21','a22','b22',...
   'a23','b23','m','a','b','c','d'});

I get the following error:

Error using fittype/testCustomModelEvaluation (line 12)
Expression (a11*sin(2*pi*x/365.25) + b11*cos(2*pi*x/365.25)+ a12*sin(4*pi*x/365.25) +
b12*cos(4*pi*x/365.25)).*(a21*sin(pi*y/12)+ b21*cos(pi*y/12) + a22*sin(pi*y/6) + b22*cos(pi*y/6) + a23*sin(pi*y/3)+
b23*sin(pi*y/3)) + m*w + (a*v.^2 + b*v + c).*u + d is not a valid MATLAB expression, has non-scalar coefficients, or cannot be
evaluated:
Not enough inputs to FITTYPE function.

Error in fittype>iCreateFittype (line 371)
    testCustomModelEvaluation( obj );

Error in fittype (line 328)
                obj = iCreateFittype( obj, varargin{:} );

Note that this is an extension of a fit I was creating earlier with success which was 3-dimensional fit with no u,v, or w dependence and without the associate coefficients. Despite my best efforts, I have been unable to find my syntax error in this relatively simple extension. Is there something simple and/or important I'm missing?