Amazon Europe Web Services - Invalid Ids Presented

I am trying to connect to Amazon Web Services Europe. I have opened an account with Amazon for Europe and I obtained and AWSAccessKeyId and an AWSSecretKey for Amazon Europe. My customer has sent over their Amazon Europe credentials. Is something wrong with my request?

Request

POST http://ift.tt/19zikZA HTTP/1.1
User-Agent: CloudCartConnector/1 (Language=C#; CLI=4.0.30319.18444;  Platform=Win32NT/6.1.7601.65536; MWSClientVersion=2014-09-30)
Content-Type: application/x-www-form-urlencoded; charset=utf-8
Host: mws-eu.amazonservices.com
Content-Length: 359
Expect: 100-continue
Connection: Keep-Alive

AWSAccessKeyId=XX&Action=ListOrders&LastUpdatedAfter=2015-03-31T20%3A31%3A38Z&LastUpdatedBefore=2015-03- 31T20%3A31%3A52Z&MarketplaceId.Id.1=XX&SellerId=XX&Signature=XX&SignatureMethod=HmacSHA256&SignatureVersion=2&Timestamp=2015-03-31T20%3A36%3A52Z&Version=2013-09-01

Response

<?xml version="1.0"?>
<ErrorResponse xmlns="http://ift.tt/PeLt2L">
 <Error>
<Type>Sender</Type>
<Code>InvalidParameterValue</Code>
<Message>Invalid ids presented</Message>
 </Error>
 <RequestId>7f89f886-b946-43d6-8bf5-bda9d03df186</RequestId>
</ErrorResponse>