Paypal Payment Errors

yesterday my hosting company do a migration to nother servers.

suddenly all paypal transactions got errors

usually after my customer pay item using paypal..
they back to my website with instant download (order proceeded)

now suddenly got errors,

Customer redirect back from paypal to my site,but the Status Order still (Open).

Response: Access Denied

Access Denied

You don't have permission to access "" on this server.

Reference #18.7faef50.1491512015.ecc6520

please help