Hi Nick,
Unplug all your devices PA2s etc and try it again, otherwise you may need to set the Aquaero into 'Recovery Mode' before you update the firmware for the first time. When I first received my Aquaero, it wouldn't update either until I followed the procedure here:
http://martinsliquidlab.org/2011/12/20/a…ew-guide-wip/5/
Once I had done this, the Aquaero would update the firmware and I haven't needed to repeat this procedure with successive firmware updates.
Hope this helps.