Why am I getting a dimension error

??? Error using ==> cat CAT arguments dimensions are not consistent.

Here is the picture I am supposed to split in 3 parts which i have done

http://i580.photobucket.com/albums/ss249/turktezel/00858v_zpsccbb1246.jpg

now I want to align it but whenever I try I get the error message above

This is how I initially divided my images

figure(1);

b = imread('cw2.jpg');
imshow(b)

[rmax, cmax] = size(b)

part1 = b(1:341, 1:396);                              
imshow(part1)
part2 = b(341:683, 1:396);                            
imshow(part2)
part3 = b(683:1024, 1:396);                            
imshow(part3)

Apparently I am supposed to get the images to the exact size or I will get this error

but whenever I try and get the images to the exact size using decimal points such as 341.33333333333333 or 682.66666666666667, I get a warning message saying

basically i found the size of the picture using this

[rmax, cmax] = size(b)

rmax =

        1024

cmax =

   396

so I want 396 to stay

but I want to split the image 3 times from x axis to i divide 1024

[Walter Roberson]

You cannot select down to anything smaller than 1 pixel, so make all of them 341.

For the dimension error, we need to see your cat()