Hi megas
This behaviour can have mainly 2 reasons:
1. in jOpenSim global config the default user level is set to disabled
2. jOpenSimRegister's new parameter is set to "Joomla Activation" in advanced tab
As for 2nd, if Joomla's user options is set to "self activation", jOpenSimRegister will enable the OpenSim account automatically as soon as the user activates his/her Joomla account. If manual activation is set, the plugin will enable it as soon as an admin activates the users account.
Greetz
FoTo50