I do not recommend using paypal payments standard for creating a store that sells downloadable goods.
the issue is that paypal payments standard is not a real time payment gateway, the order needs to be stored in the database before the user is transferred to paypal. with payments standard, you need to set the status of the order to pending when the order is first inserted.
Paypal standard uses a system called IPN to post the results of the transaction to your site when the transaction is processed, you need to create a page that will act on this ipn post to update the order status:
paypal payments standard and IPN is one of the more difficult gateway options to configure correctly.
I recommend using payments pro instead, payments pro is a real time solution.
for the error on the detail page, edit the wadaorders recordset
create a new parameter:
default Value: -1
Run Time Value: $_GET['OrderID']
for the download center page, double check that the users id is being stored in the orders.oderUserID column
and add the following code after the <body> tag of the download center page to show the recordset SQL"
<?php echo"SQL: ".$query_limit_WADAorders); ?>