I was seen during my Joomla instalation that I got an error:

Session save path Unwriteable
/var/XXXXXXX/php/session

I looked via SSH and saw that the user permits are:
root : apache

probably this is what is causing this error?

Nop, I try changing it and had the same error

I try uninstalling and reinstalling the Joomla, CB and Plugins and had the same error

Can some one help me, no one can register on my page

Well... I reinstalled Joomla and CB 1.2 and worked fine, the problem aprears to be when you upgrade from CB 1.1 to 1.2.

You get sessions errors