Hi Adrian,
According to the information you provided, I’d like to confirm whether the Office for Mac worked before you updated to OS X Maverick. How did you activate the software before, by product key or Office 365 account?
Meanwhile, could you please check whether your account has been assigned the license for Office 365 Pro Plus? If you are not the admin, please contact the admin in your organization to confirm the licenses you have been assigned.
Thanks,
August