Once a "hard" change of the IP address for the domain or subdomain has been made in the customer center it can take up to 2 weeks till this modification is known to every provider. During this time inaccessability of your homepage can be the result, i.e. depending on the access provider your pages can be called up (or not) using the new IP address. This happens because of the refreshing period of the so called DNS zones or the DNS cache of the access provider which takes place once or several times per week.