there, suddenly, my client's blog on multisite stopped

hi there,
suddenly, my client's blog on multisite stopped mapping domain. i went to the database and removed mapped domain, then tried to add in wp-admin, but it gives me 'Domain name is unavailable to access' message.
i have wordpress and all plugins up to date. sunrise.php updated too.

i went to 'who is' and typed in my client's domain there. there's a notice: Important Dates - Updated on 2nd Nov.
i can see name servers there and they still point to my server so i don't understand what could have get changed that has caused this issue.

any ideas how this issue could be resolved?

thanks,
Adam