服务器错误！.htaccess 文件出现错误 500

我使用Opencart购物系统并拥有此.htaccess文件：

# STARTNITRO
RewriteRule .* - [E=HTTP_IF_MODIFIED_SINCE:%{HTTP:If-Modified-Since}]
ExpiresActive On
#CSS JS XML TXT - 1 WEEK
<FilesMatch "'.(xml|txt|css|js)$">
Header set Cache-Control "max-age=604800, public"
ExpiresDefault "access plus 1 week"
</FilesMatch>
#JPG JPEG PNG GIF SWF SVG - 1 MONTH
<FilesMatch "'.(jpg|jpeg|png|gif|swf|svg|JPG|JPEG|PNG|GIF|SWF|SVG)$">
Header set Cache-Control "max-age=2674800, public"
ExpiresDefault "access plus 1 month"
Header set Last-Modified "Wed, 05 Jun 2009 06:40:46 GMT"
</FilesMatch>
#OTF WOFF TTF ICO PDF FLV - 1 MONTH
<FilesMatch "'.(otf|ico|pdf|flv|woff|ttf)$">
Header set Cache-Control "max-age=2674800, public"
ExpiresDefault "access plus 1 month"
</FilesMatch>
# ENDNITRO
# STARTCOMPRESSNITRO
RewriteCond %{SCRIPT_FILENAME} !-d
RewriteRule ^('/?((catalog)|(assets)).+)'.css$ assets/style.php?l=9&p=$1&c=604800 [NC,L]
RewriteCond %{SCRIPT_FILENAME} !-d
RewriteRule ^('/?((catalog)|(assets)).+)'.js$ assets/script.php?l=9&p=$1&c=604800 [NC,L]

现在，当我看到我的页面时，我看到错误：

Server error! The server encountered an internal error and was unable to complete your request. Either the server is overloaded or there was an error in a CGI script.If you think this is a server error, please contact the webmaster. Error 500

如何修复此错误？！