Message Validation failure

Hi,

I have a response message within soapUI Pro 3.5.1 which, when I validate, returns 'line -1:null'. The Response message is:

<soap:Envelope xlmns:soap="http://www.w3org/2003/05/soap-envelope">
<soap:Header/>
<soap:Body>
</soap:Body>
</soap:Envelope>

Pretty simple message, eh? This error is also returned when I run the Testcase too,, but under my Schema Compliance assertion (which fails as a result). Any ideas as to what the error means and how I fix it, please?

Thanks.