C# XML Deserializing Error: Namespace prefix 'xsd' is not defined

I am trying to deserialize an XML element that I received from a SOAP response, but I am getting the "Namespace prefix 'xsd' is not defined" error. What's the possible solution for this?

Here's the sample response XML I'm getting:

<ns0:response xmlns:ns0="http://sample.site.com">
                <ns0:additionalData>
                    <ns0:entry>
                        <ns0:key xsi:type="xsd:string">Test Key</ns0:key>
                        <ns0:value xsi:type="xsd:string">1</ns0:value>
                    </ns0:entry>
                    <ns0:entry>
                        <ns0:key xsi:type="xsd:string">Test Code</ns0:key>
                        <ns0:value xsi:type="xsd:string">1</ns0:value>
                    </ns0:entry>
                </ns0:additionalData>
                <ns0:mpiData>
                    <ns1:authenticationResponse xmlns:ns1="http://sample.site2.com">Y</ns1:authenticationResponse>
                </ns0:mpiData>
            </ns0:response>

I'm deserializing it this way:

XDocument xDocument = XDocument.Parse(responseText);

var responseElement = xDocument.Descendants().Where(a => a.Name.LocalName == response.ElementName).Select(a => a).Last();

            TResponse response = default(TResponse);

            Stream memoryStream = new MemoryStream();

            responseElement.Save(memoryStream);
            memoryStream.Seek(0, SeekOrigin.Begin);

            var serializer = new XmlSerializer(typeof(TResponse));

            using (XmlReader xmlReader = XmlReader.Create(memoryStream))
            {
                response = (TResponse)serializer.Deserialize(xmlReader);
            }

            return response;