velleman k8048 programmer

[namlet]

HI

I have built this programmer and all works fine except ICSP does not seem to function (can not read and write chip) .I am using a test circuit by MICROCHIP running at 20 mhz (on board crystal) which works with another (Wilhelm) programmer. the chip I am trying to program is a 16f877/A I am using the high voltage programming method and the software appears to suggest that every thing is o.k. but the chip(s) do not read or write !........any ideas please?

Thanks

AJ