Error: Undeclared namespace prefix x:
<p>I am a SOAP newbie and struggling with how to resolve this error message,</p>

<blockquote>
  <p>{:error, "500",      "Undeclared namespace prefix \"x\"\n at [row,col
  {unknown-source}]: [1,168]"}</p>
</blockquote>

<p>for the below SOAP envelope.  Because of terms and conditions of the host system I am trying to access, I have replaced identifying URL and credential info with "xxx" and removed the majority of objects.</p>

<pre><code>&lt;x:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/"
            xmlns:read="urn://xxx/sdk/ReadObject" 
            xmlns:obj="http://xxx/object"&gt;
    &lt;x:Header&gt;
        &lt;wsse:Security xmlns:wsse="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd"
                       xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd"&gt;
            &lt;wsse:UsernameToken&gt;
                &lt;wsse:Username&gt;xxx&lt;/wsse:Username&gt;
                &lt;wsse:Password Type="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-username-token-profile-1.0#PasswordText"&gt;xxx&lt;/wsse:Password&gt;
            &lt;/wsse:UsernameToken&gt;
        &lt;/wsse:Security&gt;
    &lt;/x:Header&gt;
    &lt;x:Body&gt;
      &lt;read:readEstimate&gt;
        &lt;read:estimate&gt;
        &lt;obj:id&gt;38945&lt;/obj:id&gt;
        &lt;/read:estimate&gt;
      &lt;/read:readEstimate&gt;
    &lt;/x:Body&gt;
&lt;/x:Envelope&gt;
</code></pre>