It’s now all re-installed and works just fine again! Tried different variations of hardware and software but I couldn’t provoke it to fail again. There are no problems leaving the programmer connected all the time, the PIC starts running as soon as the programmer is finished. Only difference now is a slightly newer version of MPLAB the 8.10. I have followed Bruce advice to create two copies of a simple program and store one of them in a safe place if (God forbid!) it ever happens again.

Wayne>
Once I made a mistake using an NC micro switch on one of the pins used by the programmer and the programming failed. I can imagine some programmers can when connected disturb the PIC in a similar way. When I discovered my mistake I just needed to push and hold the switch while the programmer was running and it worked fine. (I took me awhile to find it though!).

Thank you very much guys for being here!