Adjustment request includes a negative value. For help fixing this, see http://sellercentral.amazon.co.uk/gp/help/25321
This error occurs when one of the refund components in an adjustments feed (XML) or tab-delimited adjustments file is a negative value. Refund components must be a positive value representing the refund amounts you wish applied to the order.
You cannot charge a customer's credit card by supplying a negative value. For more information on charging additional fees to a customer, please see the answer to How can I re-charge a customer's credit card?
To resolve this error resubmit your adjustment data with positive refund values.