Okay, I compared all the fuses and found out this one locks it up:
@ __CONFIG _CONFIG2L, _PWRT_ON_2L & _BOR_OFF_2L & _BORV_27_2L
It is hex 08, if I change it to hex 0F all is fine. Has to do with the brown-out settings. Could be the brown out voltage or the brown-out ON/OFF bit. Don't want to destroy another chip (my last one) so will leave it for now. But weird it is, is there any way to unlock these chips?
Thank you,
Kees