Can be bizarre issues like this - I have to use com2 if I use windows although I have nothing trying to use com1, and believe me - I have checked. I put it down to standard Microsoft nonsense and accept the fact that I have to hook my nokia stuff in through com 1 now.
A brief liaison with XP (yes I know, but I had to have a quick play to see just how insecure it was) showed the same scenario, but Linux copes fine with any of com1 - com4.
My advice - accept that MS will never be "sensible" and prepare for workarounds
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Rory
MkIIa, blue lit buttons, memory upgrade, 1Tb in Subaru Forester STi
MkII, 240Gb in Mark Lord dock
MkII, 80Gb SSD in dock