Multiple Payments Generate ~ XML Postback

First, I am running with aMember 4.2.14.3b7ee0a

We use "ultracart" for payment and in the XML Postback, we do get this error on Ultracart Logs:

Here's the Error Log

Code:

-- getBeginDate() done ---
The UltraCart order item had a quantity of 1, and the aMember product has a configured quantity of 1, so the product of those two values is 1.  This will be the quantity used.
submitting POST to this url: [http://xyz.com/amember/api/invoices]
payload=[_key=some_secret_key&_format=xml&user_id=17969&paysys_idmanual&currency=USD&first_subtotal=297&first_period=2037-12-31&rebill_times=0&second_subtotal=0&second_period=&is_confirmed=1&status=1&nested[invoice-items][0][item_id]=13&nested[invoice-items][0][item_type]=product&nested[invoice-items][0][item_title]=Test+Product&nested[invoice-items][0][item_description]=Test+Description&nested[invoice-items][0][qty]=1&nested[invoice-items][0][first_price]=297&nested[invoice-items][0][first_period]=2037-12-31&nested[invoice-items][0][rebill_times]=0&nested[invoice-items][0][second_price]=0&nested[invoice-items][0][second_period]=&nested[invoice-items][0][currency]=USD&nested[invoice-items][0][billing_plan_id]=13&nested[invoice-payments][0][user_id]=17969&nested[invoice-payments][0][paysys_id]=manual&nested[invoice-payments][0][transaction_id]=PLM-201401211010-200680&nested[invoice-payments][0][receipt_id]=UltraCart+XYZ-201401211010-200680+item&nested[invoice-payments][0][currency]=USD&nested[invoice-payments][0][amount]=297&nested[access][0][user_id]=17969&nested[access][0][product_id]=13&nested[access][0][transaction_id]=XYZ-201401211010-200680&nested[access][0][begin_date]=2037-12-31&nested[access][0][expire_date]=2037-12-31]
--- createPayment() response follows: ---
 
------------------------------------------
createPayment response was not a valid xml response containing an invoice.  assuming failure.
One or more item payments failed.  Setting overall status to FAILURE for this order.
END PROCESSING ORDER ID XYZ-201401211010-200680

In aMember we do get the following 2 errors:

Code:

EXCEPTION during unsubscribe user 4180 from list 2
Failed loading NewsletterList(2)

I am not sure how to fix this error and which "user" is it referencing and which "newsletter".

Hence, its creating multiple payments and the "customers" gets to know as if they were charged "n" times.

Please do let help me out!

Thank you very much!