Zen cart, paypal issue and cookie

Hello this is message that i have when I want to do a test purchase on my zen cart site with paypal. Below is the message that I have having. I have same issue and some of my customers are having the same issue as well and will abandon the cart in the last step of the purchase. Can anyone help me for that. If you have not fix issue like that before then don't bid. i dont want new freelancer. I dont have big budget, and so I am paying $15 for this. Now if you fix me this problem, I have plenty of other work that you can help with and I will award you without posting here again. Thanks for the help. Once you fix it, i will test with payment again. also, i dont thing this is issue with my browser because many customer have abandon cart because of issue "Sorry — your last action could not be completed. If you were making a purchase or sending money, we recommend that you check both your PayPal account and your email for a transaction confirmation after 30 minutes. If you came to this page from another website, please return to that site (don't use your browser's Back button) and restart your activity. If you came from PayPal's website, click the PayPal logo in the upper-left corner to return to our home page and restart your activity. You might have to log in again."