Retail Point of Sales - Pay by Customer Account - Error

Hello,

I am having the  following error message when try to pay Customer Account on my POS.

Error

Microsoft.Dynamics.Retail.Pos.Customer.Customer: System.NullReferenceException: Object reference not set to an instance of an object.
at LSRetailPosis.TransactionServices.InvokeMethod(Nullable`1 timeout, String methodName, Object[] parameters)
at LSRetailPosis.TransactionServices.Invoke(Nullable`1 timeout, String methodName, Object[] parameters)
at LSRetailPosis.TransactionServices.Invoke(String methodName, Object[] parameters)
at Microsoft.Dynamics.Retail.Pos.Customer.Customer.GetCustomerBalances(String customerId, String invoiceCustomerId).

Microsoft.Dynamics.Retail.Pos.Customer.Customer: System.NullReferenceException: Object reference not set to an instance of an object.
at LSRetailPosis.TransactionServices.InvokeMethod(Nullable`1 timeout, String methodName, Object[] parameters)
at LSRetailPosis.TransactionServices.InvokeMethodNoDataReturn(Boolean& retValue, String& comment, String methodName, Object[] parameterList)
at LSRetailPosis.TransactionServices.ValidateCustomerStatus(Boolean& valid, String& comment, String customerId, Decimal amount, String currencyCode)
at Microsoft.Dynamics.Retail.Pos.Customer.Customer.AuthorizeCustomerAccountPayment(Boolean& valid, String& comment, String& manualAuthenticationCode, String customerId, Decimal amount, IRetailTransaction retailTransaction).

All configurations/setup have been done for this payment method.

Can anyone help?

Zaheen