Thanks, unfortunately need it tonight as the device ships tomorrow(sic).However, I fixed it by making a new serialport object and cribbing a config file from the test program that came with the ppm.

I realised that it was only working after I had run that particular test.
Every time I thought "Hey it works", it was immediately after running the test program then going back to my original file incomprehensibly.

So, I guess I'm a litle bit the wiser now...