Java – content not allowed in prolog exception

I am trying to send xml to a java-based web service given to me by a third party via a c#.NET application, and I get the org.xml.sax.SAXParseException: Content is not allowed in prolog error.

I have verified the xml against the schema, and I passed the memorystream I am using to hold the xml to an .xml file, then opened the file with a hex editor to make sure that there were no undesired characters in the prolog, and there are none. When opened, the first characters in the file are

<?xml version="1.0" encoding="utf-8"?>

The class I was given to use to send the xml data to the web service accepts a byte array. I figure that creating the xml using an XmlTextWriter to a utf-8 encoded memorystream, then sending the contents of the stream to a byte array is the most direct method.

I have done a lot of research and tried all the possbilities around this issue that I could find, but nothing works. Could someone please help? Thanks in advance.

By the way, here is a portion of what the web service returns to me. In the payload of the SOAP message, should the data after the element look like that, or be readable xml like the content before it?

Messages:
Message:

Payload: <?xml version="1.0" encoding="utf-8"?><soap:Envelope xmlns:soap="http:/
/schemas.xmlsoap.org/soap/envelope/" xmlns:xsi="http://www.w3.org/2001/XMLSchema
-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"><soap:Body><postSubmissi
on xmlns="http://service.arm.hud.gov/"><submissionHeader><agcHcsId>1</agcHcsId><
agcName>test</agcName><systemName>123</systemName><cmsSubId>123456</cmsSubId><su
bFlag>0</subFlag></submissionHeader><agcType>test</agcType><submissionData>PD94b
WwgdmVyc2lvbj0iMS4wIiBlbmNvZGluZz0idXRmLTgiPz48dG5zOlN1Ym1pc3Npb25EYXRhIHhzaTpzY
2hlbWFMb2NhdGlvbj0iaHR0cDovL2dvdi5odWQuYXJtL2FybV9kYXRhYmFnXzNfMS54c2QiIHhtbG5zO
nhzaT0iaHR0cDovL3d3dy53My5vcmcvMjAwMS9YTUxT......etc............................
</submissionData></postSubmission></soap:Body></soap:Envelope>

Here the xml data for better readability:

<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:soap="http:/
    /schemas.xmlsoap.org/soap/envelope/"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema
    -instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
    <soap:Body>
        <postSubmissi on xmlns="http://service.arm.hud.gov/">
            <submissionHeader>
                <agcHcsId>1</agcHcsId>
                <agcName>test</agcName>
                <systemName>123</systemName>
                <cmsSubId>123456</cmsSubId>
                <subFlag>0</subFlag>
            </submissionHeader>
            <agcType>test</agcType>
            <submissionData>PD94b
                WwgdmVyc2lvbj0iMS4wIiBlbmNvZGluZz0idXRmLTgiPz48dG5zOlN1Ym1pc3Npb25EYXRhIHhzaTpzY
                2hlbWFMb2NhdGlvbj0iaHR0cDovL2dvdi5odWQuYXJtL2FybV9kYXRhYmFnXzNfMS54c2QiIHhtbG5zO
                nhzaT0iaHR0cDovL3d3dy53My5vcmcvMjAwMS9YTUxT......etc............................
            </submissionData>
        </postSubmission>
    </soap:Body>
</soap:Envelope>