Also had this issue… You can modify line 168 of nextend-facebook-connect.php to something like this to fix it:
$sanitized_user_login = sanitize_user($new_fb_settings[‘fb_user_prefix’] . preg_replace(‘/[^A-Za-z0-9\-]/’, ”, strtolower($user_profile[‘first_name’]) . strtolower($user_profile[‘last_name’])));
This works great however, it leaves no space inbetween the first and last name. Is there a way to put a space, dot or dash?
