[Plugin: Register Plus] Changing custom fields

I added a new custom field to the registration form (license_id). I can read it using:

global $userdata;
get_currentuserinfo();
$licenseid = get_user_option(‘license_id’,userdata->ID);

But I can not change it. I am tring:

$newvalue = $licenseid;
$option = ‘license_id’;
update_user_option($userdata->ID,$option,$newvalue,true);

but it doesn’t seem to store the new value. Any suggestions.

Thanks.