If you're new to Maemo it'll be hard to help you, since you need to be an experienced N900 user to use Yappari,

Anyway here it goes: First check that you're using Yappari 0.0.27 (last version). Then most registration issues is because people didn't set the time & date correctly in their phone, or that they don't know their own phone number in international format (country code + phone number).

If your phone has the CORRECT date & time and you're 100% sure that you're entering your phone number correctly, then you have to send me the log, which is in /home/user/.config/scorpius/yappari.log. This is something people new to Maemo can't do easily, and without the log I can't help any further.