A couple of problems here.
MySQL doesn't support subqueries.
You are trying to add 1 to a query result set, not a field value!
You need a sepqrate query to find the max value
$sql4 = "select max(member_id) as maxid from member";
$result4 = mysql_query($sql4);
$row = mysql_fetch_array($result4);
$NewMemberId = $row["maxid"] + 1;