CDMA based using multiple PN sequences embeded into whole object

hii everyone

 I am trying to run this watermark embedding code. my cover image size is 512x512, watermark image is 64x64 and key image is also having size is 64x64.
clear all;
% save start time
start_time=cputime;

k=2;                % set the gain factor for embeding

% read in the cover object
file_name='lena.tif';
cover_object=double(imread(file_name));

% determine size of watermarked image
Mc=size(cover_object,1);  %Height
Nc=size(cover_object,2);  %Width

% read in the message image and reshape it into a vector
file_name='watermark1.bmp';
message=double(imread(file_name));
Mm=size(message,1);                          %Height
Nm=size(message,2);                          %Width
message_vector=round(reshape(message,Mm*Nm,1)./256);

% read in key for PN generator
file_name='key.bmp';
key=double(imread(file_name))./256;

% reset MATLAB's PN generator to state "key"
rand('state',key);

watermarked_image=cover_object;

% when message contains a '0', add pn sequence with gain k to cover image
for kk=1:length(message_vector)
    pn_sequence=round(2*(rand(Mc,Nc)-0.5));

      if message(kk) == 0
          watermarked_image=watermarked_image+k*pn_sequence;
      end
  end
% convert back to uint8
watermarked_image_uint8=uint8(watermarked_image);

% write watermarked Image to file
imwrite(watermarked_image_uint8,'cdma_watermarked.bmp','bmp');

% display processing time
elapsed_time=cputime-start_time,

% % calculate the PSNR
% psnr=psnr(cover_object,watermarked_image_uint8,Mc,Nc),

% display watermarked Image
figure(1)
imshow(watermarked_image_uint8,[])
title('Watermarked Image')

but i am getting following error message after executing code

??? Error using ==> reshape
To RESHAPE the number of elements must not change.

Error in ==> TEST12 at 22
message_vector=round(reshape(message,Mm*Nm,1)./256);