Error with my square and multiply algorithm

So basically I have to implement a 32-bit version of RSA. However there's a problem with the SaM algorithm, which is the following:

function result = SquareAndMultiply(exponent,basis,modulus)

result = 1;

while exponent>0
    if mod(exponent,2)==1
        result = mod(result.*basis, modulus);
    end

      basis = mod(basis.*basis, modulus);
      exponent = fix(exponent/2);

end

end

It shows that the encrypted message I decrypted is not equal to the original message, which began when the primes are 14 bits in size (before if it's 13 bits or less it works fine), which makes the modulus be 28 bits in size.

Anyone knows what happened here?

EDIT: It seems the value of n plays a role here.