Question: "Error, (in series/function) improper op or subscript selector"

I tried using 'maple tag' but the preview came out bad. So here's a clipboard copy of my maple code:

> f := proc (x, d) options operator, arrow; (1/4)*Pi*x^6-(3/5)*Pi*x^5+(1/60)*(30*x^3-72*x^2+80)*arctan(d/sqrt(x^2-d^2))*x^3+(2/3)*Pi*x^3+(1/60)*d*sqrt(x^2-d^2)*(16*d^4+x*(8*x-27)*d^2+2*x(3*x^3-9*x^2+20))-(1/60)*d(27*d^2-40)^3*log(x+sqrt(x^2-d^2)) end proc;
print(`output redirected...`); # input placeholder
          1     6   3     5   1  /    3       2     \       /      d      \  3
(x, d) -> - Pi x  - - Pi x  + -- \30 x  - 72 x  + 80/ arctan|-------------| x
          4         5         60                            |    / 2    2\|   
                                                            \sqrt\x  - d //   

     2     3
   + - Pi x
     3      

     1        / 2    2\ /    4                 2      /   3      2     \\
   + -- d sqrt\x  - d / \16 d  + x (8 x - 27) d  + 2 x\3 x  - 9 x  + 20//
     60                                                                  

                     3                       
     1   /    2     \     /        / 2    2\\
   - -- d\27 d  - 40/  log\x + sqrt\x  - d //
     60                                      
> mtaylor(f(x, d), [x = 0, d = 0], 4);
%;
Error, (in series/function) improper op or subscript selector

How do I fix this error?