hello thomas
this is a quite a common problem faced by many designers when using RXX series aserik has suggested refer to errata sheet on Philips site.
Also try one of this thing see if it helps u.
firstly,
check EA pin is tied high i.e to Vcc
make the psen bar pin low i.e gnd when u want to program the I.C.

In WINISP
select the IC no.,frequency (the exact value of crystal frequency)
and do the blank check.

If the communication fails(by decreasing of baud rate which u may see in the WIN ISP s/w)
there's some problem with ur h/w or
Pls try to reset the controller and try once again this time u may succeed

BEST OF LUCK
satyajeet pardeshi