My login history shows Failed: Assertion Invalid 
The SAML Assertion Validator says Unable to parse the response
XMLSpy says Unable to locate a reference to a supported schema type (DTD, W3C Schema) within this document instance.

I generate this response with C# and have used it in a previous project without problems. Any ideas on what I'm missing/doing wrong?

<samlp:Response ID="_E27F438B33756518E90C7E3AC535B439" Version="2.0" IssueInstant="2011-10-06T11:55:47Z" Destination="https://test.salesforce.com" xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol">
	<saml:Issuer Format="urn:oasis:names:tc:SAML:2.0:nameid-format:entity" xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion">https://www.salesforce.com</saml:Issuer>
	<Signature xmlns="http://www.w3.org/2000/09/xmldsig#">
		<SignedInfo>
			<CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/>
			<SignatureMethod Algorithm="http://www.w3.org/2000/09/xmldsig#rsa-sha1"/>
			<Reference URI="#_E27F438B33756518E90C7E3AC535B439">
				<Transforms>
					<Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature"/>
					<Transform Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#">
						<InclusiveNamespaces PrefixList="#default saml ds xs xsi" xmlns="http://www.w3.org/2001/10/xml-exc-c14n#"/>
					</Transform>
				</Transforms>
				<DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
				<DigestValue>En5W1EvQScxxBQRO7YHZO9rhitE=</DigestValue>
			</Reference>
		</SignedInfo>
		<SignatureValue>UQoEZIb9tEOmIsIsRIuxmR5m3PkTSAuvo2O4IZFetDLImgdLcyEgyFJMzLraYGDE2rwuh+CrXBDAiOQITXACZJzvlmu1J9LkS58yIhWR3ueuRCO9E/4qB0C6NVm+sMg8cLghri5Tkrmw/yEwjdxYpNhoK3C1FGLw6/vDWuMrUBQ=</SignatureValue>
		<KeyInfo>
			<X509Data>
				<X509Certificate>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</X509Certificate>
			</X509Data>
		</KeyInfo>
	</Signature>
	<samlp:Status>
		<samlp:StatusCode Value="urn:oasis:names:tc:SAML:2.0:status:Success"/>
	</samlp:Status>
	<saml:Assertion Version="2.0" ID="_64A96C56928D068794CC29675229BC6E" IssueInstant="2011-10-06T11:55:47Z" xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion">
		<saml:Issuer Format="urn:oasis:names:tc:SAML:2.0:nameid-format:entity">https://www.salesforce.com</saml:Issuer>
		<saml:Subject>
			<saml:NameID Format="urn:oasis:names:tc:SAML:1.1:nameid-format:unspecified">user@company.com</saml:NameID>
			<saml:SubjectConfirmation Method="urn:oasis:names:tc:SAML:2.0:cm:bearer">
				<saml:SubjectConfirmationData NotOnOrAfter="2011-10-06T12:05:47Z" Recipient="https://test.salesforce.com"/>
			</saml:SubjectConfirmation>
		</saml:Subject>
		<saml:Conditions NotOnOrAfter="2011-10-06T12:05:47Z">
			<saml:AudienceRestriction>
				<saml:Audience>https://saml.salesforce.com</saml:Audience>
			</saml:AudienceRestriction>
		</saml:Conditions>
		<saml:AuthnStatement AuthnInstant="2011-10-06T11:55:47Z">
			<saml:AuthnContext>
				<saml:AuthnContextClassRef>urn:oasis:names:tc:SAML:2.0:ac:classes:unspecified</saml:AuthnContextClassRef>
			</saml:AuthnContext>
		</saml:AuthnStatement>
	</saml:Assertion>
</samlp:Response>