RSA encrption Help

Can someone please help me with understanding RSA encryption. Starting small I can encrypt and decrypt using:
P = 11
q = 3
e = 3

and
p=17, q=11, e=7

However when I try p = 257, q=263, e = 7, Letter for Encrption = R (ascii 82).
I can't get it to work. I am using BigInt to do all of the math - attached is all of my code - can anyone tell where I have gone wrong

Cheers

Rob

output:
p=17, q=11, e=7
N= 67591
C=59156

phi:67072
d:38327
C^d:433370372864891793361365563191187492639486140446836071782674040345154835633626032994202073684903 505243341240218748940410
M:64415 - wrong