Error encounterred regarding sympoly when using polyfitn

Hi, I am using MATLAB 2007b. I wish to use polyfitn to model a set of data with 3 independent var and 1 dependent var. I have downloaded both the polyfitn and sympoly. When i used them in MATLAB, it returned error as below (where try_raw_ind is the name of my script file): ..............................................................................

??? Error: File: sympoly.m Line: 27 Column: 17

Undefined function or variable 'protected'.

Error in ==> polyn2sympoly at 44

sp = sympoly(sp);

Error in ==> try_raw_ind at 34

polyn2sympoly(p)

...............................................................................

Could you help me - what does this mean and how to overcome this.

Thank you very much.

Sincerely,

CY ______________________________________________________________________________________

For your infor, the code of 'try_raw_ind.m' is as below:

%3 independent variables

t=[13, 14, 15, 17, 31, 31, 31, 31, 31, 33, 40, 39, 39, 39, 42];

x=[0.023757, 0.030813, 0.029581, 0.030750, 0.059712, 0.028538, 0.026890, 0.057410, -0.008362, 0.035928, 0.034209, 0.043282, 0.034579, 0.013274, -0.008294];

y=[0.063693, -0.000839, -0.083547, 0.112831, -0.009965, -0.000985, -0.001612, 0.011356, -0.004155, 0.133603, -0.000626, 0.001079, -0.001705, 0.031965, -0.094755];

%1 dependent variable

s=[34.33, 34.36, 34.44, 32.17, 29.62, 30.34, 30.34, 30.34, 30.72, 30.00, 30.83, 31.18, 30.82, 30.02, 30.97];

%start polyfitn

t=t'; x=(1.7 + x)'; y=(110.3 + y)'; s=s';
%xy = [x,y];

p = polyfitn([t,x,y],s,2)

if exist('sympoly') == 2
    polyn2sympoly(p)
end

if exist('sym') == 2
    polyn2sym(p)
end