The line below produces a vector of size 501.
t = 0:(1/(samples*f0)):T;
repmat repeats the 1X501 matrix 5 times along the row making it 1X2505 size vector.So s has 1X2505 dimension.
The line below produces a vector of dimension 1X2501.
t = 0:(1/(samples*f0)):N*T;
So there is mismatch in sizes of s and t.Therefore you get the error mentioned.