Are you sure about 0xf800 ?? I can see you are mistaking the boot code for the IAP code interface. Erik's code uses the IAP interface to set the boot vector. What you are trying to do is jump to the same code that is jumped to when PSEN is low during reset. Be sure that you have the correct address. AND, be sure about that ENBOOT flag. I don't see it in any of my datasheets, so I don't know what it does. But if it is not in the default for AUXR after reset, you don't need it.