htaccess Issue : Header throwing 404 although page is correctly displayed – Oscommerce

I am facing quite a strange problem at the moment, I have wordpress and oscommerce installations on single domain. I placed wordpress at the root and oscommerce in /store/ folder.
Everything is working properly except one thing. The server headers of oscommerce are throwing a 404 error although the page is displayed correctly. This results in a situation that googlebot will not index these pages at all.
Can anybody help me to resolve this issue? What should I do now?

Root httaccess is 

RemoveHandler .html .htm
AddType application/x-httpd-php .php .htm .html

RewriteEngine On
RewriteCond %{HTTP_HOST} ^outdoorwatersolutions.com [NC]
RewriteRule ^(.*)$ http://www.outdoorwatersolutions.com/$1 [L,R=301]


<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

and oscommerce httaccess is

Options +SymLinksIfOwnerMatch
<IfModule mod_rewrite.c>
 RewriteEngine On

 # RewriteBase instructions
 # Change RewriteBase dependent on how your shop is accessed as below.
 # http://www.mysite.com = RewriteBase /
 # http://www.mysite.com/catalog/ = RewriteBase /catalog/
 # http://www.mysite.com/catalog/shop/ = RewriteBase /catalog/shop/

 # Change RewriteBase using the instructions above 
 RewriteBase /store/
 RewriteRule ^([a-z0-9/-]+)-p-([0-9]+).html$ product_info.php [NC,L,QSA]
 RewriteRule ^([a-z0-9/-]+)-c-([0-9_]+).html$ index.php [NC,L,QSA]
 RewriteRule ^([a-z0-9/-]+)-m-([0-9]+).html$ index.php [NC,L,QSA]
 RewriteRule ^([a-z0-9/-]+)-pi-([0-9]+).html$ popup_image.php [NC,L,QSA]
 RewriteRule ^([a-z0-9/-]+)-pr-([0-9]+).html$ product_reviews.php [NC,L,QSA]
 RewriteRule ^([a-z0-9/-]+)-pri-([0-9]+).html$ product_reviews_info.php [NC,L,QSA]
 # Articles contribution
 RewriteRule ^([a-z0-9/-]+)-t-([0-9_]+).html$ articles.php [NC,L,QSA]
 RewriteRule ^([a-z0-9/-]+)-au-([0-9]+).html$ articles.php [NC,L,QSA]
 RewriteRule ^([a-z0-9/-]+)-a-([0-9]+).html$ article_info.php [NC,L,QSA]
 # Information pages
 RewriteRule ^([a-z0-9/-]+)-i-([0-9]+).html$ information.php [NC,L,QSA]
 # Links contribution
 RewriteRule ^([a-z0-9/-]+)-links-([0-9_]+).html$ links.php [NC,L,QSA]
 # Newsdesk contribution
 RewriteRule ^([a-z0-9/-]+)-n-([0-9]+).html$ newsdesk_info.php [NC,L,QSA]
 RewriteRule ^([a-z0-9/-]+)-nc-([0-9]+).html$ newsdesk_index.php [NC,L,QSA]
 RewriteRule ^([a-z0-9/-]+)-nri-([0-9]+).html$ newsdesk_reviews_info.php [NC,L,QSA]
 RewriteRule ^([a-z0-9/-]+)-nra-([0-9]+).html$ newsdesk_reviews_article.php [NC,L,QSA]
</IfModule>