Problem with on product page " This error (HTTP 500 Internal Server Error)

[han08]

hello. so many thanks for prestashop staff and other helpers.
i got problem.

when i installed 1.4 shop then most things good.
but click on products then error " This error (HTTP 500 Internal Server Error) means that the website you are visiting had a server problem which prevented the webpage from displaying."

also same problem other website on my own.

www.wholesaleremote.com

Thanks again

Mark
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Server information

Prestashop Version: 1.4.0.17
Server information: Linux #1 SMP Wed Feb 23 10:03:17 MST 2011 x86_64
Server software Version: Apache
PHP Version: 5.2.17
MySQL Version: 5.1.47-community-log
URL of your website: http://www.clickerwholesale.com/
Theme name used: prestashop

[han08]

error message on screen

Fatal error: Class 'QuantityDiscount' not found in /home2/homekore/public_html/clickerwholesale/modules/quantitydiscounts/quantitydiscounts.php on line 38

[han08]

another website error message are

Fatal error: Uncaught exception 'SmartyCompilerException' with message 'Syntax Error in template "/home2/homekore/public_html/wholesaleremote/themes/prestashop/category.tpl" on line 1 "{include file=$tpl_dir./breadcrumb.tpl}" - Unexpected "/", expected one of: "{" , "$" , "identifier" , INTEGER' in /home2/homekore/public_html/wholesaleremote/tools/smarty/sysplugins/smarty_internal_templatecompilerbase.php:431 Stack trace: #0 /home2/homekore/public_html/wholesaleremote/tools/smarty/sysplugins/smarty_internal_templateparser.php(2855): Smarty_Internal_TemplateCompilerBase->trigger_template_error() #1 /home2/homekore/public_html/wholesaleremote/tools/smarty/sysplugins/smarty_internal_templateparser.php(2920): Smarty_Internal_Templateparser->yy_syntax_error(37, '/') #2 /home2/homekore/public_html/wholesaleremote/tools/smarty/sysplugins/smarty_internal_smartytemplatecompiler.php(51): Smarty_Internal_Templateparser->doParse(37, '/') #3 /home2/homekore/public_html/wholesaleremote/tools/smarty/sysplugins/smarty_internal_template in /home2/homekore/public_html/wholesaleremote/tools/smarty/sysplugins/smarty_internal_templatecompilerbase.php on line 431