Si, puede ser lo que dice Suky.
Igualmente he visto este error con MPLAB con Pickit originales, miren:
http://www.microchip.com/forums/tm.aspx?m=398671Agrego:
MPLAB IDE: PK2Error0028: Unable to Enter Debug Mode
There are many reasons this error may be encountered. Some things to check are:
1. The part may require an ICD Header for debugging. See the Header Specification (available in the Downloads section of the PICkit 2 webpage) for information on which parts need headers and which header to get. Note that to connect PICkit 2 to a debug header, an RJ-11 to ICSP adapter is required.
2. If the part does not have an internal oscillator, or an external oscillator is selected in the Configuration bits, it must be connected to a working oscillator in order to debug the part. If there is no oscillator, the part cannot execute code and won't enter Debug Mode.
3. Make sure to select Debugger > Program in MPLAB before trying to run or step your code. The part won't run without code programmed into it.
4. Also check to be sure your code is not trying to use reserved areas of program memory or the File Registers. See section 4.1.2 of the most recent revision of the PICkit 2 User's Guide. (available in the Downloads section of the PICkit 2 webpage)
5. 4.7k Ohm pulldown resistors are required on the ICSPx/PGx signal lines for reliable operation. If your PICkit 2 has a black pushbutton (R3 or older), these resistors need to be added (See this thread for more information). If your PICkit 2 has a red pushbutton (R4 or newer), these resistors are already connected internally to the PICkit 2 so nothing need be done.