I've also got a Power Tower/Z4 bus setup and at one stage I had all sorts of problems with it.
Apart from the possibility of the Z4 connector shorting on its support screw, which I insulated, I started getting random crashes. It took a while to recognise that the problems were due to the poor quality of the P8/P9 connectors from the power supply.
I noticed that the white plastic was showing heat staining (brown) on several of the leads. It turned out that the flat brass springy gizzmos inside the sockets were fatigued and not making positive contact with the Z4 pins.
I dismantled the P8/P9 sockets and reset the connectors properly. I've not had any problems since.
Cheers,
JaX
