Simply put, you need to do what that page says.
AdultWork.com is required to identify the location of its users before it can allow them to transact for VAT purposes. Whether it applies or not, we need to prove that by identifying where you are accessing from. If we don't know your location, we need to ask for it.
The "Where are you?" page tells you how and why.
More information on VAT can be found on the specific pages for Service Providers and Service Seekers.