Impossible to register a new user

Hello, After installation of xwiki (+Tomcat 5 + Postgresql 8.2). I would like to realize a user registration (inscription/register) but the proposed page is the same that for the login (identification/log - in). and so i can't add user, when I try, the system answer me: "Wrong user name" In tomcat logs i find this error: 17:08:57,046 ERROR http-8080-Processor23 http://localhost:8080/xwiki/bin/register/XWiki/Register SimpleLog4JLogSystem:logVelocityMessage:154 - Left side ($objuser.getProperty("usertype").value) of '==' operation has null value. If a reference, it may not be in the context. Operation not possible. [line 10, column 66] can you help me please? Thanks, François Lion