My site is running well with submissions being paid and payments being processed by Paypal (working OK)

I recently made a 'partial refund' to a new customer, (after a small issue, which was resolved by mutual agreement by providing 50% refund)

I noticed that in the Payment Logs: Info page

this repeated entry (repeated 8 times, in the last 12 hours)

Payment Logs
Info (General payment Info)
Invalid postback: payer_id: FC*******4U verify_sign: AQ********************59Q.Sh******************4J16YmV5 residence_country: GB address_state: Highland receiver_email: info@mywebsite.com payment_type: instant address_street: 123 customer street name town address_city: customer city business: info@mywebsite.com payment_status: Refunded shipping: 0.00 payment_fee: address_country: United Kingdom charset: windows-1252 payment_date: 07:46:30 Apr 25, 2008 PDT invoice: **************** mc_fee: -0.68 receipt_id: xxxx-xxxx-xxxx-xxxx address_zip: customer post code custom: do;process_payment=1;payment_success=1 payment_gross: txn_id: ****************G last_name: customer name receiver_id: ************* item_number: address_country_code: GB parent_txn_id: xxxxxxxxxxxxxxxx payer_email: customer@email.com address_name: customer name notify_version: 2.4 mc_gross: -20.00 reason_code: refund first_name: customer name mc_currency: GBP

Any ideas?

Thanks
Colin Thompson