お世話になっております。

その後の経過として、別のVPSにて検証しております。

seasoftさんの推察どおり共用サーバーが問題のようです。
検証中のVPSでは一応プラグインが機能してますが、それでも
かなり怪しい挙動不審さが見られます。

warningだけでフロント機能に影響なければ様子見したのですが、
フロント機能でシステムエラーになる”場合が時々”あります。

■GMOクラウドVPS
・CentOS 6.2 + Plesk11
・Apache/2.2.15
・perl, v5.10.1
・mysql Ver 14.14 Distrib 5.1.61
・PHP 5.3.3



2013/04/02 14:59:00 [/index.php] Warning(E_WARNING): Invalid argument supplied for foreach() on [/var/www/vhosts/********/********/data/downloads/plugin/GaEcommerceTracking/templates/GaEcommerceTracking_header.tpl(45)] from 103.5.142.5
2013/04/02 14:59:03 [/plugin/SocialLogin/login_with_openid.php] Warning(E_WARNING): include(FacebookApiException.php) [<a href='function.include'>function.include</a>]: failed to open stream: そのようなファイルやディレクトリはありません on [/var/www/vhosts/********/********/data/class/SC_ClassAutoloader.php(120)] from 103.5.142.5
2013/04/02 14:59:03 [/plugin/SocialLogin/login_with_openid.php] Warning(E_WARNING): include(FacebookApiException.php) [<a href='function.include'>function.include</a>]: failed to open stream: そのようなファイルやディレクトリはありません on [/var/www/vhosts/********/********/data/class/SC_ClassAutoloader.php(120)] from 103.5.142.5
2013/04/02 14:59:03 [/plugin/SocialLogin/login_with_openid.php] Warning(E_WARNING): include() [<a href='function.include'>function.include</a>]: Failed opening 'FacebookApiException.php' for inclusion (include_path='/var/www/vhosts/********/********/data/module:.:') on [/var/www/vhosts/********/********/data/class/SC_ClassAutoloader.php(120)] from 103.5.142.5
2013/04/02 14:59:05 [/plugin/SocialLogin/login_with_openid.php] Warning(E_WARNING): include(FacebookApiException.php) [<a href='function.include'>function.include</a>]: failed to open stream: そのようなファイルやディレクトリはありません on [/var/www/vhosts/********/********/data/class/SC_ClassAutoloader.php(120)] from 103.5.142.5
2013/04/02 14:59:05 [/plugin/SocialLogin/login_with_openid.php] Warning(E_WARNING): include(FacebookApiException.php) [<a href='function.include'>function.include</a>]: failed to open stream: そのようなファイルやディレクトリはありません on [/var/www/vhosts/********/********/data/class/SC_ClassAutoloader.php(120)] from 103.5.142.5
2013/04/02 14:59:05 [/plugin/SocialLogin/login_with_openid.php] Warning(E_WARNING): include() [<a href='function.include'>function.include</a>]: Failed opening 'FacebookApiException.php' for inclusion (include_path='/var/www/vhosts/********/********/data/module:.:') on [/var/www/vhosts/********/********/data/class/SC_ClassAutoloader.php(120)] from 103.5.142.5
2013/04/02 14:59:06 [/plugin/SocialLogin/login_with_openid.php] Fatal error(E_USER_ERROR): on [/var/www/vhosts/********/********/data/class/SC_Response.php(182)] from 103.5.142.5
customer_id = 1
/var/www/vhosts/********/********/plugin/SocialLogin/login_with_openid.php(226): LC_Page_Plugin_LoginWithOpenID->process
/var/www/vhosts/********/********/plugin/SocialLogin/login_with_openid.php(59): LC_Page_Plugin_LoginWithOpenID->action
/var/www/vhosts/********/********/plugin/SocialLogin/login_with_openid.php(188): SC_Response->sendRedirect
/var/www/vhosts/********/********/data/class/SC_Response.php(182): trigger_error
2013/04/02 14:59:10 [/plugin/SocialLogin/login_with_openid.php] Warning(E_WARNING): include(FacebookApiException.php) [<a href='function.include'>function.include</a>]: failed to open stream: そのようなファイルやディレクトリはありません on [/var/www/vhosts/********/********/data/class/SC_ClassAutoloader.php(120)] from 103.5.142.5
2013/04/02 14:59:10 [/plugin/SocialLogin/login_with_openid.php] Warning(E_WARNING): include(FacebookApiException.php) [<a href='function.include'>function.include</a>]: failed to open stream: そのようなファイルやディレクトリはありません on [/var/www/vhosts/********/********/data/class/SC_ClassAutoloader.php(120)] from 103.5.142.5
2013/04/02 14:59:10 [/plugin/SocialLogin/login_with_openid.php] Warning(E_WARNING): include() [<a href='function.include'>function.include</a>]: Failed opening 'FacebookApiException.php' for inclusion (include_path='/var/www/vhosts/********/********/data/module:.:') on [/var/www/vhosts/********/********/data/class/SC_ClassAutoloader.php(120)] from 103.5.142.5
2013/04/02 14:59:12 [/mypage/index.php] Warning(E_WARNING): Invalid argument supplied for foreach() on [/var/www/vhosts/********/********/data/downloads/plugin/GaEcommerceTracking/templates/GaEcommerceTracking_header.tpl(45)] from 103.5.142.5