Unable to register extensions

Good morning forums, I have recently installed Asterisk 1.8 and FreePBX 2.8 onto CentOS 5.5 as per the instructions found here --> http://www.jcarle.com/2010/12/17/installing-freepbx-2-8-with-asterisk-1-8-on-centos-5-5/

Although the system is up and running, I can’t seem to register any SIP accounts/extensions.

For the “client”, I am using a Windows 7 PC with ZoIPer softphone installed. I have disabled SELinux and the Firewall on Centos and still no joy.

(I know that the ZoIPer client works as we have used it with Elastix previously)

I am sorry that I don’t know which logs to start reading on the CentOS machine to offer any ideas on where the problem could be but if you say ‘get this log by doing xyz’ then I will be more than happy to oblige.

Many thanks for your time in reading, I hope that someone can help me!