Thanks for replying and the advice.
Being a ver 1.6b, the pinheader had to be connected to the board with wire links. These all appear OK, as does the D0 and BT wires. However I'm beginning to think I may have developed some cold joints. The reason it doesn't FRAG anymore is maybe because my cleaning may have moved a wire slightly which made the connection good (probably only temporary). My problem currently is maybe a cold joint in my D0. Your idea of shorting it out should easily test this.
I had already found the link you gave me, as well as others that detail how to connect up a Duox2 chip on a pinheader.
After testing grounding the D0, I think I have to re-solder all the connections to eliminate cold joints. I haven't been looking forward to doing this, because even though I've been soldering for years, these connections are very, very small.
Thanks again.