to help troubleshoot, edit the confirm page
look for all instances of the following code (make sure to use a case sensitive search):
$WA_editCmd = mysql_query($WA_Sql, $WA_connection) or die(mysql_error());
and change it to:
$WA_editCmd = mysql_query($WA_Sql, $WA_connection) or die(mysql_error()."<br />".$WA_Sql);
then look for all instances of (also case sensitive):
$WA_editCmd = mysql_query($WA_sql, $WA_connection) or die(mysql_error());
and change it to:
$WA_editCmd = mysql_query($WA_sql, $WA_connection) or die(mysql_error()."<br />".$WA_sql);
this will add the sql command being executed after the error, post back the results of testing the checkout again.