A & B from an external PSU allso proved problematic at 9v, better at 10 and OK again at 12v. But without the hub, uploading caused problems and return serial data had dropped characters. If you hammer the Ethernet and the SD then I need at least 12v on the external supply to 'keep up'. My conclusion is there is not enough 'overhead' available on some USB ports to even drive the board enough to do uploads. I have met this problem with USB port drive abilities and other peripherals in the past. The quoted PSU range for external supply is higher than quoted even with a 2A supply at 9V, however at 12v and just 500mA drive all is OK. So at the moment to do 'in the field programming', which would be nice from just netbook, I need a good quality mains powered USB hub. Not good. I don't have a true *nix box, but from a VM on my laptop, I have the same issue as if I was talking to EM via windows. So my guess is there is on on board PSU issue with lower voltaged USB ports and the external supply can't go quite as low than about 10v or 11v. Thanks for the comments Whizz, and the heads up, as down the track I will be using both the ethernet and sd card and also a maths co-processor, LCD, encoder IC and most of the I/O so will have to monitor the power