As I mentioned in my TinySensor 1.3 PCB announcement, I have an error that prevents the ISP connector from being used. Of course, you can always take the Attiny84 out (if you use a socket) and program it with another Arduino, for example, but it is much neater to use an ISP programmer like the USBTiny ISP. So the problem was I that I need two extra resistors to keep the RESET and CS on the RFM12B high, quite easily fixable by soldering two 10K resitors just like this:
With these two fixes the ISP can now be used.