problems in vigenere square encryption algorithm

I used vignere square encryption algorithm in my code for steganography.

I took code from here :

https://in.mathworks.com/matlabcentral/fileexchange/29443-deploying-a-shared-library?focused=6789820&tab=function

But, sometimes i get the error :

Error using arrayfun Non-scalar in Uniform output, at index 16, output 1. Set 'UniformOutput' to false.

Error in decrypt (line 19) plaintext = arrayfun(@(m,n) find(v(m,:) == n), k, ciphertext) - 1;

How can i resolve this error?