nanasessさん、ご返信ありがとうございます。
下記この様にエラーが表示されます。

＞data/logs/site.log へ出力されていると思います.

すみません、知識が浅いため上記の内容が見方などよく分かりません、site.log 〜site.log5まで有りましたが、何を示しているのか分かりません。コレは、エラーが出力される場所なのですか？

http://〇〇.com/eccube/html/admin/products/product_class.php

SERVER_ADDR:
REMOTE_ADDR:64.134.243.10
USER_AGENT:Mozilla/5.0 (Windows; U; Windows NT 5.1; ja; rv:1.9.2.3) Gecko/20100401 Firefox/3.6.3 (.NET CLR 3.5.30729)

SELECT class_id1, class_id2, name1, name2, rank1, rank2, product_class_id, product_id, T1_classcategory_id AS classcategory_id1, T2_classcategory_id AS classcategory_id2, product_code, stock, stock_unlimited, sale_limit, price01, price02, status FROM ( SELECT T1.class_id AS class_id1, T2.class_id AS class_id2, T1.classcategory_id AS T1_classcategory_id, T2.classcategory_id AS T2_classcategory_id, T1.name AS name1, T2.name AS name2, T1.rank AS rank1, T2.rank AS rank2 FROM dtb_classcategory AS T1, dtb_classcategory AS T2 WHERE T1.class_id IN (SELECT class_id1 FROM
(SELECT T1.class_id1, T1.class_id2, T1.classcategory_id1, T1.classcategory_id2, T2.product_id,
T1.name1, T1.name2, T2.product_code, T2.stock, T2.price01, T2.price02, T1.rank1, T1.rank2
FROM (SELECT T1.class_id AS class_id1, T2.class_id AS class_id2, T1.classcategory_id AS classcategory_id1, T2.classcategory_id AS classcategory_id2, T1.name AS name1, T2.name AS name2, T1.rank AS rank1, T2.rank AS rank2
FROM dtb_classcategory AS T1, dtb_classcategory AS T2 ) AS T1 LEFT JOIN dtb_products_class AS T2
ON T1.classcategory_id1 = T2.classcategory_id1 AND T1.classcategory_id2 = T2.classcategory_id2, T1.size2, ) AS crs_prd WHERE product_id = ? GROUP BY class_id1, class_id2) AND T2.class_id IN (SELECT class_id2 FROM
(SELECT T1.class_id1, T1.class_id2, T1.classcategory_id1, T1.classcategory_id2, T2.product_id,
T1.name1, T1.name2, T2.product_code, T2.stock, T2.price01, T2.price02, T1.rank1, T1.rank2
FROM (SELECT T1.class_id AS class_id1, T2.class_id AS class_id2, T1.classcategory_id AS classcategory_id1, T2.classcategory_id AS classcategory_id2, T1.name AS name1, T2.name AS name2, T1.rank AS rank1, T2.rank AS rank2
FROM dtb_classcategory AS T1, dtb_classcategory AS T2 ) AS T1 LEFT JOIN dtb_products_class AS T2
ON T1.classcategory_id1 = T2.classcategory_id1 AND T1.classcategory_id2 = T2.classcategory_id2, T1.size2, ) AS crs_prd WHERE product_id = ? GROUP BY class_id1, class_id2)) AS T1 LEFT JOIN (SELECT * FROM dtb_products_class WHERE product_id = ?) AS T3 ON T1_classcategory_id = T3.classcategory_id1 AND T2_classcategory_id = T3.classcategory_id2 ORDER BY rank1 DESC, rank2 DESC
DB Error: syntax error

SELECT class_id1, class_id2, name1, name2, rank1, rank2, product_class_id, product_id, T1_classcategory_id AS classcategory_id1, T2_classcategory_id AS classcategory_id2, product_code, stock, stock_unlimited, sale_limit, price01, price02, status FROM ( SELECT T1.class_id AS class_id1, T2.class_id AS class_id2, T1.classcategory_id AS T1_classcategory_id, T2.classcategory_id AS T2_classcategory_id, T1.name AS name1, T2.name AS name2, T1.rank AS rank1, T2.rank AS rank2 FROM dtb_classcategory AS T1, dtb_classcategory AS T2 WHERE T1.class_id IN (SELECT class_id1 FROM
(SELECT T1.class_id1, T1.class_id2, T1.classcategory_id1, T1.classcategory_id2, T2.product_id,
T1.name1, T1.name2, T2.product_code, T2.stock, T2.price01, T2.price02, T1.rank1, T1.rank2
FROM (SELECT T1.class_id AS class_id1, T2.class_id AS class_id2, T1.classcategory_id AS classcategory_id1, T2.classcategory_id AS classcategory_id2, T1.name AS name1, T2.name AS name2, T1.rank AS rank1, T2.rank AS rank2
FROM dtb_classcategory AS T1, dtb_classcategory AS T2 ) AS T1 LEFT JOIN dtb_products_class AS T2
ON T1.classcategory_id1 = T2.classcategory_id1 AND T1.classcategory_id2 = T2.classcategory_id2, T1.size2, ) AS crs_prd WHERE product_id = '199' GROUP BY class_id1, class_id2) AND T2.class_id IN (SELECT class_id2 FROM
(SELECT T1.class_id1, T1.class_id2, T1.classcategory_id1, T1.classcategory_id2, T2.product_id,
T1.name1, T1.name2, T2.product_code, T2.stock, T2.price01, T2.price02, T1.rank1, T1.rank2
FROM (SELECT T1.class_id AS class_id1, T2.class_id AS class_id2, T1.classcategory_id AS classcategory_id1, T2.classcategory_id AS classcategory_id2, T1.name AS name1, T2.name AS name2, T1.rank AS rank1, T2.rank AS rank2
FROM dtb_classcategory AS T1, dtb_classcategory AS T2 ) AS T1 LEFT JOIN dtb_products_class AS T2
ON T1.classcategory_id1 = T2.classcategory_id1 AND T1.classcategory_id2 = T2.classcategory_id2, T1.size2, ) AS crs_prd WHERE product_id = '199' GROUP BY class_id1, class_id2)) AS T1 LEFT JOIN (SELECT * FROM dtb_products_class WHERE product_id = '199') AS T3 ON T1_classcategory_id = T3.classcategory_id1 AND T2_classcategory_id = T3.classcategory_id2 ORDER BY rank1 DESC, rank2 DESC [nativecode=1064 ** You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ') AS crs_prd WHERE product_id = '199' GROUP BY class_id1, class_id2) AND T2.cla' at line 6]

D:\CustomerData\webspaces\webspace_00120487\wwwroot\eccube\html\admin\products\product_class.php 34:LC_Page_Admin_Products_ProductClass_Ex->process
D:\CustomerData\webspaces\webspace_00120487\wwwroot\eccube\data\class_extends\page_extends\admin\products\LC_Page_Admin_Products_ProductClass_Ex.php 56:LC_Page_Admin_Products_ProductClass->process
D:\CustomerData\webspaces\webspace_00120487\wwwroot\eccube\data\class\pages\admin\products\LC_Page_Admin_Products_ProductClass.php 127:LC_Page_Admin_Products_ProductClass->lfGetClassCatListEdit
D:\CustomerData\webspaces\webspace_00120487\wwwroot\eccube\data\class\pages\admin\products\LC_Page_Admin_Products_ProductClass.php 299:SC_Query->getall
D:\CustomerData\webspaces\webspace_00120487\wwwroot\eccube\data\class\SC_Query.php 156:SC_DbConn->getAll
D:\CustomerData\webspaces\webspace_00120487\wwwroot\eccube\data\class\SC_DbConn.php 164:DB_common->getAll
D:\CustomerData\webspaces\webspace_00120487\wwwroot\eccube\data\module\DB\common.php 1610:DB_common->execute
D:\CustomerData\webspaces\webspace_00120487\wwwroot\eccube\data\module\DB\common.php 959:DB_mysql->simpleQuery
D:\CustomerData\webspaces\webspace_00120487\wwwroot\eccube\data\module\DB\mysql.php 324:DB_mysql->mysqlRaiseError
D:\CustomerData\webspaces\webspace_00120487\wwwroot\eccube\data\module\DB\mysql.php 894:DB_common->raiseError
D:\CustomerData\webspaces\webspace_00120487\wwwroot\eccube\data\module\DB\common.php 1853:PEAR->raiseError
D:\CustomerData\webspaces\webspace_00120487\wwwroot\eccube\data\module\PEAR.php 557:DB_Error->DB_Error
D:\CustomerData\webspaces\webspace_00120487\wwwroot\eccube\data\module\DB.php 893:PEAR_Error->PEAR_Error

上のようなエラーがシステムエラー画面に表示されます。
お手数ですが、どのような原因でしょうか？また、解決法など、お教え下されば幸いです。お願いします。