shutta様。
お返事ありがとうございます。

利用環境を載せます。
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[EC-CUBE] 2.12.0新規
[レンタルサーバ] RapidSite
[OS] Red Hat Enterprise Linux ES release 4 (Nahant Update 4)
[PHP] PHP Version 5.2.17
[データベース] MySQL 5.5.9
[WEBサーバ] Apache/2.0.64 (Red Hat)

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====================
PHP情報はzlibの文字列がある部分を抜粋して載せます。
====================

Registered PHP Streams compress.bzip2, dict, ftp, ftps, gopher, http, https, imap, imaps, ldap, ldaps, pop3, pop3s, rtsp, scp, sftp, smtp, smtps, telnet, tftp, php, file, data, zip, compress.zlib, MDB2LOB

Registered Stream Filters convert.iconv.*, bzip2.*, string.rot13, string.toupper, string.tolower, string.strip_tags, convert.*, consumed, zlib.*

----------------------------------------------------
curl

cURL support enabled
cURL Information libcurl/7.23.1 OpenSSL/0.9.7a zlib/1.2.3 c-ares/1.7.5 libidn/1.24 libssh2/1.3.0
----------------------------------------------------
zlib

ZLib Support enabled
Stream Wrapper support compress.zlib://
Stream Filter support zlib.inflate, zlib.deflate
Compiled Version 1.2.1.2
Linked Version 1.2.3

Directive Local Value Master Value
zlib.output_compression On On
zlib.output_compression_level -1 -1
zlib.output_handler no value no value
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お手数おかけしますが、よろしくお願いします。