Caretaker,
Could be. Make sure you select PIC18F24J10 for the PIC type in the programming tool. Also if you are using the J1Sys Adapter, make sure you are using the correct jumpers (not sure what those would be!) I programmed mine directly on the tester for both that I built. Make sure that the if you are programming directly on the board, that the PicKit is seated correctly. I had to slightly bend my 6 pin connector on the board so that the PicKit did not hit the PIC chip itself.
Good luck!
Kurt