Century Gothic Font Gone

I have been building my new website with iweb09. In the last week when I try to open a page, I get a message saying that the font century gothic, century gothis bold and century gothic italic is missing. How can this happen and how can I get it back? I have searched all over - there is nothing listed in my font book. If I say ok in iweb and keep typing it types in century gothic but if I try and open the font it is not listed except in recently used
Thank you for any help that you can provide.