Open and edit the Microchip header file P18F4620.INC. Comment out DEBUG, and save the
file. That will get rid of the error.

LVDCON EQU H'0FD2'
OSCCON EQU H'0FD3'
; DEBUG EQU H'0FD4' ; <--- comment this out & save
T0CON EQU H'0FD5'
TMR0L EQU H'0FD6'