I'm using cart66lite and have i am also using one shortcode on one page: [checkout_paypal]. It does not work. The other shortcodes for "add to cart" etc. work so that leads me to believe that there is something wrong with the code in your plugin in that respects. To be more specific, the written code nor the rendered paypal button shows on the published page.
I don't have many plugins but have deactivated them and even erased the entire site and rebuilt at one point, so that's not the issue. I've also edited in HTML, that didn't work either. I challenge anyone to help me fix this issue because it seems that no one else has been able to, i've posted a few other times. If anyone has any other ideas, great. If not, i urge the developer to look into this. Why would the other shortcodes work but not the paypal ones?