NO! You can't just change the variable to BANK1!
That variable must be in BANK0.

Both DT_INTS-18 and VirtualPort.bas fit quite comfortably in an 18F87J50, with room to spare. Even when using PBPL.

How many variables have you declared in BANK0 in your program?
Or, what other include files are you using that may have variables placed in BANK0.