The type of transaction you were performing and when the error occurred in the business process will determine if you will be charged.
Transaction charged to your account
If the error occurred after the business process was complete (e.g. registration or search request), the transaction will be charged to your account.
If you resend the identical request (with the same message ID), a standard response will be sent to you. This transaction will not result in a new charge to your account.
If you send the same request with a different message ID, your account will be charged. You will not be given a refund for this type of transaction.