I added a try-catch block to the password routine. I found after copying an article from the internet that it contained two utf-16 characters. Utf-16 along with a few other have a continuation bit. Since the Convert.ToByte method can't handle them I explicitly converted them then continued pass the exception.
So far my largest file test has been to encrypt a .MOV file that was 6,047,946,752 bytes in size using a pssword that was 10,638 bytes in size.The encryption took 3min. 46 sec. to encrypt and the same to decrypt.