Add to shopping cart button not working

Using version 1.3.9f. When the button is clicked I get the following message instead of an item being added to the cart.
" Error 404 - Not found
Your browser can't find the document corresponding to the URL you typed in."

Here is the link shown at the bottom of the browser when I highlight the button.

"mystore/index.php?main_page=product_info&cPath=612_613_614&products_id=13380&action=add_product"
which looks correct to me compared to another active site I have.

so far I have checked the files and filesizes of the working store against this one and all files containing "shopping_cart" are there and are the same size.

Any help would be greatly appreciated.
thanks,

A link will be necessary to help you, we cannot see and pull information needed to troubleshoot this.

~Melanie

thanks for the reply
The link to the site is
https://www.agilityservices.net/agilitysupply

Because you are redirecting from /agilitysupply/ to /AGILITYSUPPLY/

If you intend to use the all caps version (Very NOT recommended) then your Zen cart 2 configure files must reflect this, you cannot just redirect the requests.

~Melanie

What should I use all lower case for "agilitysupply"? Why does this matter so I will know the rules next time?

Well usability and compatibility is better without the caps... either way you cannot redirect it, Zen Cart has to match.

~Melanie

I just created a new website and I installed new version. Then I got an error 404 - Not found
Your browser can't find the document corresponding to the URL you typed in.
Any help would be greatly appreciated.
Below is the link to the site:
www.avctreasure.com

I don't see any products in your store. Have you disabled them?