In order to use our standard shopping cart display that appears as an overlay within your own sales pages, you need to copy and paste at least one block of our Cart Script code into every page that has any number of our Cart buttons.
If the overlay-style cart cannot work for any reason in a given page, the Cart buttons on that page should still work in "fallback" mode by displaying the cart in a popup window/tab. However, due to the way browsers handle cookies, items added to the overlay-style cart will not appear in the fallback/popup cart, nor vice-versa; if you're seeing that problem, check the affected sales pages to make sure every page has your cart appearing as an overlay on every page, or opening a popup window/tab from every page, not some combination of both between one sales page vs. another.
That "fallback" behavior may also happen if you have pasted our code incorrectly, like breaking a single line of code into a multiple lines while pasting it, or if your Web page editor altered our button-code HTML after you pasted it in, which may sometimes garble an important part of our code. You might want to View Source on your page and find the button code there to compare to the original button code issued in your E-junkie Dashboard.