Sale not processing after plugnpay cc approval

I have Zen Cart v1.5.1 on Linux server running PHP v5.2
using PlugnPay_cc_ss ver 1.3.8

I have everything customized and working perfectly except, when payment is approved and returns to zen cart, the items purchased remains in the shopping cart and the sale is not recorded or completed in Zen Cart.

The Merchant and Customer get confirmation emails of completed sale. The sale even completes with the Merchant account provider but zen cart is left in the dark as far payment for shopping cart items. It acts as if the user just navigated away from the cart.

I've seen this mentioned in other cases in the forums, but their solutions did not help me. All my files have the correct permissions, I have tried renaming my admin directory, etc.

Any help?

I don't know what PlugnPlay is, but the symptoms you describe sound like a known problem with Paypal Standard. The solution there is to switch to Paypal Express.