Open your contact list in Windows Live Mail, click "All contacts," select one of the contacts listed, press Ctrl + A, and then press Delete. You can then import your latest contacts without the obsolete and duplicate entries.
Hope this helps,
I was trying to import my .wab from Outlook Express into Live Mail, when I realized I had imported an old book. I found the new one and imported it. Rather than replacing contacts, it doubles them all. I have 7,000....so rather than delete each duplicate, I would rather delete the ENTIRE contact book (I know I can in Thunderbird) but I can't find a way to do that in Windows Live Mail. Suggestions anyone?