OrderAcknowledgement not working (error 25)

I am trying to submit my orderacknowledgement in aws scratchpad but i seem to get the following error:
"We are unable to process the XML feed because one or more items are invalid. Please re-submit the feed."
With errorcode: 25 I might be overlooking something but i can't figure out what because as far as i can tell the xml is made as the scheme says it should. The Scheme can be found here: Scheme Can anyone see what is wrong with the xml?

<?xml version="1.0" encoding="UTF-8"?>
<AmazonEnvelope xmlns:xsi="http://ift.tt/ra1lAU" xsi:noNamespaceSchemaLocation="amzn-envelope.xsd">
    <Header>
        <DocumentVersion>1.01</DocumentVersion>
        <MerchantIdentifier>xxxxxxxxxxxxxxxxxx</MerchantIdentifier>
    </Header>
    <MessageType>OrderAcknowledgement</MessageType>
    <Message>
        <MessageID>1</MessageID>
        <OrderAcknowledgement>
            <AmazonOrderID>xxx-xxxxxxx-xxxxxxx</AmazonOrderID>
            <MerchantOrderID>xxxxxxx</MerchantOrderID>
            <StatusCode>Success</StatusCode>
            <Item>
                <AmazonOrderItemCode>xxxxxxxxxxxx</AmazonOrderItemCode>
                <MerchantOrderItemID>xxxxxx</MerchantOrderItemID>
            </Item>
        </OrderAcknowledgement>
    </Message>
</AmazonEnvelope>