Seems there is a problem with the query then.
Find:
Code
$adduser = mysql_query("INSERT INTO `members` (`username`, `password`, `email`, `userlevel`) VALUES('$username','$password','$email','2')");
Replace with:
Code
$adduser = mysql_query("INSERT INTO `members` (`username`, `password`, `email`, `userlevel`) VALUES('$username','$password','$email','2')") or die(mysql_error());
Find:
Code
$adduser = mysql_query("INSERT INTO `members` (`username`, `password`, `email`) VALUES('$username','$password','$email')");
Replace with:
Code
$adduser = mysql_query("INSERT INTO `members` (`username`, `password`, `email`) VALUES('$username','$password','$email')") or die(mysql_error());
This will make the two queries return with errors if one is found.