SOAP Envelope can not have children other than SOAP Header and Body when calling HTTPS service

I have an HTTPS SOAP service that I'm trying to call via SoapUI.  My request looks like this:

 

<soap:Envelope xmlns:soap="http://www.w3.org/2003/05/soap-envelope" xmlns:urn="urn:com-softwareag-entirex-rpc:RSSA">
<soap:Header/>
<soap:Body>
<urn:RSSA000S/>
</soap:Body>
</soap:Envelope>

 

 

however the response I always get back is:

 

<soapenv:Envelope xmlns:soapenv="http://www.w3.org/2003/05/soap-envelope">
<soapenv:Body>
<soapenv:Fault>
<soapenv:Code>
<soapenv:Value>Sender</soapenv:Value>
</soapenv:Code>
<soapenv:Reason>
<soapenv:Text xml:lang="en-US">SOAP Envelope can not have children other than SOAP Header and Body</soapenv:Text>
</soapenv:Reason>
<soapenv:Detail/>
</soapenv:Fault>
</soapenv:Body>
</soapenv:Envelope>

 

I'm not sure why this is. Even when I remove the urn:RSSA000S child, the error is the same.

Advice is appreciated.