SIP Config wont register

Hello everyone!

We are running openfire on a windows server. Additionally, we have a Lucent Control Platform with a feature server 5 k running as our sip server. We do not use XMPP. I can not et my client to register and when I test settings it says User not authorized. Yet I can easily register the same credentials with a free client called ZOIPER. I do not even see my registration requests getting to our server. As I am new to this, what is XMPP, and do we have to have a presence of XMPP to utilize the SIP plugin in Openfire. We are on Openfire 3.5.1 and Sip Plugin is 1.0.3. Any ideas?