We recently switched from PayPal Standard to PayPal Express and PayPal Pro. Client is now getting a few duplicate orders and almost all show in Zen Cart without any of the order data. See screenshot:

Name: paypal-data-missing.png Views: 481 Size: 8.7 KB

I've enabled dedugging and is seems this is the problem, but I don't understand what it means or how to fix it.

May-06-2015 13:03:19 (1430935399)
before_process - EC-5
resultset:
Array
(
[TIMESTAMP] => 2015-05-06T18:03:19Z
[CORRELATIONID] => e18e1d5611ff6
[ACK] => Failure
[VERSION] => 61.0
[BUILD] => 16566018
[L_ERRORCODE0] => 10415
[L_SHORTMESSAGE0] => Transaction refused because of an invalid argument. See additional error messages for details.
[L_LONGMESSAGE0] => A successful transaction has already been completed for this token.
[L_SEVERITYCODE0] => Error
[CURL_ERRORS] =>
)