problems with alphasim

Hi, I am trying to run alphasim and keep getting the following error message: I've tried various masks. The error below was after I applyed the brain mask dparsfa created. Any help is much appreciated.

REST Version: 1.5, Release: 20101101
??? Undefined function or method 'normrnd' for input arguments of type 'double'.

Error in ==> rest_AlphaSim at 61
fim=normrnd(0,1,nx,ny,nz);

Error in ==> rest_AlphaSim_gui>pushbuttonrun_Callback at 55
rest_AlphaSim(mask,outdir,outname,rmm,fwhm,pthr,iter);

Error in ==> gui_mainfcn at 96
feval(varargin{:});

Error in ==> rest_AlphaSim_gui at 27
gui_mainfcn(gui_State, varargin{:});

??? Error while evaluating uicontrol Callback

??? Undefined function or method 'normrnd' for input arguments of type 'double'.

Error in ==> rest_AlphaSim at 61
fim=normrnd(0,1,nx,ny,nz);

Error in ==> rest_AlphaSim_gui>pushbuttonrun_Callback at 55
rest_AlphaSim(mask,outdir,outname,rmm,fwhm,pthr,iter);

Error in ==> gui_mainfcn at 96
feval(varargin{:});

Error in ==> rest_AlphaSim_gui at 27
gui_mainfcn(gui_State, varargin{:});

??? Error while evaluating uicontrol Callback