Just thought i'd let you know... I received and e-mail from Lucasarts after I sent them pics/scans of my CD's/Manual/cd-key etc.
They have issued me with a new cd-key.... this works perfectly in multiplayer. If any one else has this problem (and i think there are a few) just contact Lucasarts tech support... they do answer the e-mails.
Have a good xmas all!