Whew, had me worried there for a minute.

In order for the Include file to create the correct size working variables ...
The PRECISION constant needs to be BEFORE the include file.

Code:
PRECISION CON 8 SYSTEM  	' 8 bytes = 64-bit
INCLUDE "N-Bit_Math.pbp"	' Include Alexander Avtanski's Multibyte Arithmetic 
				' Assembly Library Wrapped for PBP by Darryl Taylor
				' Version:1.3 Beta (1/7/2010)
It was creating Working vars of only 1 byte, instead of 8 bytes.
After moving the constant, I got all the correct results with your program.

HTH,