Error using imwrite Expected DATA to be non empty ???what is wrong with my code ???

what is the problem and the solution of this problem . if I removed the line of imwrite it works and framing all the letters but I need to crop the letters and saves them for the next steps

while(j<m)
    while(i<n)
       rectangle('position',[i  j  60  115] , 'LineWidth',1,'EdgeColor','red');
       i= i+70; %45
       i= i+1;
       ccc = imcrop(crop , [i  j  60  115 ]);
        % str=sprintf('image%d.fig',i);
        % saveas(gcf,str);
       imwrite(ccc,strcat('hh',num2str(vv),'.bmp'));
       vv=vv+1;    
       s=s+i;
    end
     j= j+120; %58
     i= 1 ;
     j= j+1 ;
  end