feval error with window function

Error using feval Argument must contain a string or function_handle.

Error in window (line 54) w = feval(wname,N,varargin{:});

and this is a window function which is used in my project:

        function varargout = window(wname,N,varargin)
    %WINDOW Window function gateway.
    %   WINDOW(@WNAME,N) returns an N-point window of type specified
    %   by the function handle @WNAME in a column vector.  @WNAME can
    %   be any valid window function name, for example:
    %
    %   @bartlett       - Bartlett window.
    %   @barthannwin    - Modified Bartlett-Hanning window. 
    %   @blackman       - Blackman window.
    %   @blackmanharris - Minimum 4-term Blackman-Harris window.
    %   @bohmanwin      - Bohman window.
    %   @chebwin        - Chebyshev window.
    %   @flattopwin     - Flat Top window.
    %   @gausswin       - Gaussian window.
    %   @hamming        - Hamming window.
    %   @hann           - Hann window.
    %   @kaiser         - Kaiser window.
    %   @nuttallwin     - Nuttall defined minimum 4-term Blackman-Harris window.
    %   @parzenwin      - Parzen (de la Valle-Poussin) window.
    %   @rectwin        - Rectangular window.
    %   @taylorwin      - Taylor window.
    %   @tukeywin       - Tukey window.
    %   @triang         - Triangular window.
    %
    %   WINDOW(@WNAME,N,OPT1,OPT2) designs the window with the optional input
    %   arguments specified in OPT1 and OPT2. To see what the optional input
    %   arguments are, see the help for the individual windows, for example,
    %   KAISER or CHEBWIN.
    %
    %   WINDOW launches the Window Design & Analysis Tool (WinTool).
    %
    %   EXAMPLE: 
    %      N  = 100;
    %      w  = window(@blackmanharris,N);
    %      w1 = window(@gausswin,N,2.5);
    %      w2 = window(@taylorwin,N,5,-35);
    %      plot(1:N,[w,w1,w2]); axis([1 N 0 2]);
    %      legend('Blackman-Harris','Gaussian','Taylor');
    % 
    %   See also BARTLETT, BARTHANNWIN, BLACKMAN, BLACKMANHARRIS, BOHMANWIN, 
    %            CHEBWIN, GAUSSWIN, HAMMING, HANN, KAISER, NUTTALLWIN, PARZENWIN, 
    %            RECTWIN, TAYLORWIN, TRIANG, TUKEYWIN, WINTOOL.

    %    Author(s): P. Costa 
    %    Copyright 1988-2008 The MathWorks, Inc.
    %    $Revision: 1.14.4.2 $  $Date: 2008/07/09 18:13:44 $ 

    if nargin == 0,
        wintool;

        w = [];

     else
        % Create an N-point window specified in wname
        error(nargchk(2,inf,nargin,'struct')); 

% Function handle and order are required
      w = feval(wname,N,varargin{:});
  if nargout > 0,
      varargout{1} = w;
  end

    % [EOF]
    end

[Walter Roberson]

Please show your call to window()

[gasmi]

This is a call to window() function

mask_use = window (mask_code, chipsamples, length(mask_code)/chipsamples, floor(Tm/dt), floor(Tm/dt)*P_gain);