What is the URL for the .wordpress.com blog you are trying to domain mapping from?
What is the URL for the domain that you are trying to domain map to?
Did you properly designate the primary domain URL as per step 5. these instructions?
To activate your new domain, select the button next to the one you wish to activate and click Update Primary Domain. Your blog will be accessible from both of these domains; the Primary Domain is what actually appears as your domain within the address bar of web browsers. If you do not see your blog at the new domain immediately, please allow some time for the DNS changes to propagate.
Do you know if it takes time for the new address to start working?
It can take up to 72 hours for a domain name change to propagate throughout the internet and we have no control over when DNS caches are cleared. I'm in Canada and your domain name change is already live for me.