In some cases it is not possible to reprogram PIC's of which the PGC and PGD pins are used by the PIC program for outputting a "1" (and are as such cannot be controlled by the K8048 programmer any more).
This thread http://forum.microchip.com/tm.aspx?m=347029
suggests to drive the PGC and PGD lines harder. This can be done by short circuiting R4 and R8 in the K8031 programmer (or build in a very much lower value than 1K -- I have 8R2 now --).
Anyway, it works
but should be avoided
(The PIC will try to deliver a rather high current into T1 and T2) I think