Please note that there are three include files in the above code which are required for it to operate.

N-BIT_Math.pbp
At its core is the Multibyte Arithmetic Assembly Library that was written by Alexander Avtanski.
The Assembly Library was wrapped for PBP by Darrel Taylor [Version:1.3 Beta (JAN 07,2010)]
This library is used to assemble the 64-Bit high precision math,
You can find reference to it in this PB Forum Thread:
http://www.picbasic.co.uk/forum/showthread.php?t=12433

DT_INTS-18.bas & ReEnterPBP-18.bas
DT_INTS-18.bas is Darrel Taylor's Base Interrupt System for PIC18F [Version:3.3 (MAR 24, 2008)]
ReEnterPBP-18.bas is Darrel Taylor's PBP interrupts for PIC18F [Version:1.4 (MAR 24, 2008)]
Both can be referenced at this PB Forum Thread:
http://www.picbasic.co.uk/forum/showthread.php?t=3251
Or directly from Darrel Taylor's web page here:
http://darreltaylor.com/DT_INTS-18/home.html
Please note that there are different versions for (PIC12F, 14F, & 16F) and for PIC18F.

--Bob