Hi Glyn,
I had the M1 installed for quite sometime and never had any issues with the activation. However, I just formatted my OS drive and in the process of re-installing all my software (including this).
I'll post back once I'm done....(I'm also on Vista, but 32bit).
I never updated (not sure if there were any) M1 since I bought it (possibly a year ago). Were there any updates you installed on Monopoly that may have caused this?