Paypal Standard orders recorded by OpenCart as "Missing"

I am opening up a new topic for this for OpenCart 1.5.4.

Even though there are MANY similar topics on this board for various releases, I have not found any definitive answers that pertain to Paypal Standard and OpenCart 1.5.4.

I am currently using sandbox mode, although I have tested and get the same results in live mode.
Followed the directions in http://www.opencart.com/index.php?route ... h=32_35_60
to set up the seller.

The order goes through from opencart to paypal, the payment is successful, the information is sent back to Opencart and the success page is displayed. The cart is cleared and everything looks 100% great to the customer.
However, the order is shows up as "Missing" in the OpenCart Admin Orders panel.

HELP!

HI -
we are having trouble with Paypal Standard as well.

On the paypal side, the IPN is sending info back to the cart, response is code '200' - but we are not able to view orders within OC, (they are in the missing/abandoned as cancelled), nor are customers receiving emails...

there was a reference in another thread to a fix for this that had to do with encryption - it had a bad link pointing to the 'answer' - how to solve this???

thank you