There are several possible reasons:1. The domain name syntax is improper.2. The domain name has already been registered.3. The connection with central Registry database is temporarily unavailable.4. The Registry database is busy and can't handle additional requests.The central database Registry exchanges information with InterNIC.net every day at GMT 6:00-8:00 (US EST 1:00 - 3:00 AM) As a result, the central Registry and the network system are heavily loaded. The registration process is severely impacted during this time. Registration delays, failures, and other interruptions are common. If this happens to you, please wait until this two hour window has passed before trying to resume your registrations. 
We stronlgy recomend you contact our SUPPORT center for live assitance about registration failure.