Maybe you also use the old firmware in your Picstart Plus programmer?
Last summer there were a new firmware v1.50 that fix problem with programming 12cxxx and 16c5x.
Download latest MPLAB 4.12 and read the readme file for picstart plus to se how to upgrade the picstart plus.
the newest firmware for picstart I beleve is v2.01

Niklas
----- Original Message ----- 
From: Tobias <tobias@EUNET.NO>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Thursday, September 23, 1999 8:57 PM
Subject: Help! PIC12c508a programming problem..


> Hello list,
> 
> I have trouble programming the pic12c508A 04/PHBG chip. I am using same hex
> file as I have used many times before (using PIC12C508A 04/PHBN). The hex
> file uses internal osc.
> 
> I am programming using PIC start pluss and MPLAB 3.99
> I cant imagine what is wrong,
> Anyone have any clue...???
> 
> best regards,
> tobias
>