Thanks for the information, I've spent plenty of time puzzling over this one. The solution has been to get a new USB dongel for the laptop and run it that way.
Re the advantage of running a laptop and a 278 together, I've found I like the wider map view that I get from the laptop, while letting the 278 do the micro nav. I have to fiddle with the 278 less this way. Some would argue that I'm being greedy running both, but I've found that both have their time and place.
Your bang on the mark reference the 278, it is a great bit of equipment, and it is a shame about the SD card as I've not long ago paid a arm and a leg for a Garmin memory card, ouch!
Thanks for your thoughts guys, sorry it has taken so long to get back to you.