Manufacturer product list

I got an issue with the
On my manufacturer's page the buy it now links dont work as it seems to have an extra index? in the url
Example. buy it now buttons in
http://www.morganhorse.co.uk/baileys-m-4.html

for example buy it now links are supposed to
http://www.morganhorse.co.uk/index.php?products_id=3964&action=buy_now&sort=3a&manufacturers_id=4

Can anyone help me with this please?
which files need editing
I thought it was product_listing.php file and reuploaded the file and still does not work.

I use the SEO url module.
Can anyone point to me which files may be churning out the wrong code.

Thank you
Onesimpleman

I use the SEO url module.
Can anyone point to me which files may be churning out the wrong code.
This is where I would start....
Try disabling the SEO and see if they are correct then if so move to the support for the SEO module

Thank you Korai,
I disabled the seo url and it works... so the problem is seo url module ( I thought it was and I have asked this question there ..but no answers)
I cannot afford to turnoff the seo module at this point as the whole site is indexed and cannot afford to lose SERP. (which brings in sales)

But I am losing sales as people click on the fake buy it now and leave..

I think it is something to do with seo url filters.
So

Issue sorted by adding
RewriteRule ^index/?$ index.php?&%{QUERY_STRING}
to .htaccess