Seems I might have spoke to soon after all.
Tried to connect to a friends game via Direct IP connection, and depending who's hosting we both get a message along the lines of:
'Mismatch in configuration. You might want to consider putting this user on your ignore list.'
I've played a couple of online games via EA's site, and I've not had any of the exploding buildings problems etc etc, but I can't seem to chat to my opponents.... though that could be down to my incompetence.
Could my PC / his PC / whoevers PC deter that I was trying to run an online game from a clonedcd install?
Surely if I've made a 1:1 copy of disc1 (and continued the install with original disc2) there wouldn't be any difference in the two? I guess I'll have to try and run an online game from the downstairs PC with the complete original install.
I knew it wouldn't be that easy.