What is the result that you are getting versus the expected result from this? You can check on the query that is being executed by adding in a die statement like this:
<?php
$WADWCs_bygd_WADWCaldursbyti_bygd = "0";
if (isset($_SESSION['s_bygd'])) {
$WADWCs_bygd_WADWCaldursbyti_bygd = $_SESSION['s_bygd'];
}
mysql_select_db($database_manntal, $manntal);
$query_WADWCaldursbyti_bygd = sprintf("SELECT aldur AS XLABEL, m_tal AS YVALUE FROM aldursbyti_bygd WHERE ", GetSQLValueString($WADWCs_bygd_WADWCaldursbyti_byg d, "text"));
die($query_WADWCaldursbyti_bygd);
Please post back with this so we can determine what the query is that is being executed.