I am a complete newbie, so take this with a grain of salt. Maybe your cable
is too long ?  I've read messages here in the past where people were having
problems with circuits that turned out to be related to cable length.
Perhaps it has to do with the extra capacitance introduced by the cable.

Here's hoping this prompts someone more knowledgable to provide more
concise suggestions.

Eric

On Saturday, August 07, 1999 9:29 AM, Dave Johnson
[SMTP:djohnson@SIRIUS.COM] wrote:
> A followup to the 16F877 ICSP difficulties I was having:
>
> When I built my ICSP cable, I wasn't sure which Vss and Vdd pin to use on
> the programmer side: there are 2 of each. I figured they were probably
> connected internally anyway, so it wouldn't matter, but just to be "safe"
> I connected them together across the socket that gets plugged into the
> programmer before soldering on the cable.
>
> Yesterday in desperation (and in the spirit of "try anything, no matter
> how ridiculous") I snipped that connection between the Vdd and Vss pairs,
> and lo and behold, I suddenly was able to program my boards! Most of the
> time anyway. I still can't read them, strangely, so verify doesn't work,
> but programming works 9 out of 10 times.
>
> So my next newbie question is: why? Why should it matter if the Vdd and
> Vss pairs are wired together or not? And what might make my cable be able
> to program but not read the chip? RB7 is both in and out, so obviously
> the connection is fine, since the parts program.
>
> Dave Johnson