There are few mistakes in S3 class provided by Amazon toolkit.

Replace following class in your S3 class.

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public class CopyObjectResponse_element {
        public S3.CopyObjectResult CopyObjectResponse;
        private String[] CopyObjectResponse_type_info = new String[]{'CopyObjectResponse','http://s3.amazonaws.com/doc/2006-03-01/','CopyObjectResult','1','1','false'};
        private String[] apex_schema_type_info = new String[]{'http://s3.amazonaws.com/doc/2006-03-01/','true'};
        private String[] field_order_type_info = new String[]{'CopyObjectResponse'};
    }

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public S3.CopyObjectResult CopyObject(String SourceBucket,String SourceKey,String DestinationBucket,String DestinationKey,String MetadataDirective,S3.MetadataEntry[] Metadata,S3.AccessControlList AccessControlList,DateTime CopySourceIfModifiedSince,DateTime CopySourceIfUnmodifiedSince,String[] CopySourceIfMatch,String[] CopySourceIfNoneMatch,String StorageClass,String AWSAccessKeyId,DateTime Timestamp,String Signature,String Credential) {
            S3.CopyObject_element request_x = new S3.CopyObject_element();
            S3.CopyObjectResponse_element response_x;
            request_x.SourceBucket = SourceBucket;
            request_x.SourceKey = SourceKey;
            request_x.DestinationBucket = DestinationBucket;
            request_x.DestinationKey = DestinationKey;
            request_x.MetadataDirective = MetadataDirective;
            request_x.Metadata = Metadata;
            request_x.AccessControlList = AccessControlList;
            request_x.CopySourceIfModifiedSince = CopySourceIfModifiedSince;
            request_x.CopySourceIfUnmodifiedSince = CopySourceIfUnmodifiedSince;
            request_x.CopySourceIfMatch = CopySourceIfMatch;
            request_x.CopySourceIfNoneMatch = CopySourceIfNoneMatch;
            request_x.StorageClass = StorageClass;
            request_x.AWSAccessKeyId = AWSAccessKeyId;
            request_x.Timestamp = Timestamp;
            request_x.Signature = Signature;
            request_x.Credential = Credential;
            Map<String, S3.CopyObjectResponse_element> response_map_x = new Map<String, S3.CopyObjectResponse_element>();
            response_map_x.put('response_x', response_x);
            WebServiceCallout.invoke(
              this,
              request_x,
              response_map_x,
              new String[]{endpoint_x,
              '',
              'http://s3.amazonaws.com/doc/2006-03-01/',
              'CopyObject',
              'http://s3.amazonaws.com/doc/2006-03-01/',
              'CopyObjectResponse',
              'S3.CopyObjectResponse_element'}
            );
            response_x = response_map_x.get('response_x');
            return response_x.CopyObjectResponse;
        }


Hope this will help you.
Thanks,
Anil