Reading xml string with c#

I have the following soap response string:

<EncryptionInfoResponse> <Status>0</Status> <Message></Message> <ServiceID>xxxxxxx</ServiceID> <KeyID>xxxxxxxxx</KeyID> <ContentKey>xxxxxxx</ContentKey> <LicAcqURL><![CDATA[http://sldrm.licensekeyserver.com/core/rightsmanager.asmx]]></LicAcqURL> <LicUIURL></LicUIURL> <CustomXML><![CDATA[<CID>pFRCPIy87oUJtOWis7IYAA==</CID><DRMTYPE>smooth</DRMTYPE>]]></CustomXML> <ContentID>xxxxxxx</ContentID> <PRHeader><![CDATA[<WRMHEADER xmlns="http://schemas.microsoft.com/DRM/2007/03/PlayReadyHeader" version="4.0.0.0"><DATA><PROTECTINFO><KEYLEN>16</KEYLEN><ALGID>AESCTR</ALGID></PROTECTINFO><KID>xvd10JPbxh5rsS27LoCIxQ==</KID><LA_URL>http://sldrm.licensekeyserver.com/core/rightsmanager.asmx</LA_URL><DS_ID>xxxxxx</DS_ID><CUSTOMATTRIBUTES xmlns=""><CID>pFRCPIy87oUJtOWis7IYAA==</CID><DRMTYPE>smooth</DRMTYPE></CUSTOMATTRIBUTES><CHECKSUM>GKaxxISZpMs=</CHECKSUM></DATA></WRMHEADER>]]></PRHeader> </EncryptionInfoResponse>

I want to get the values of "KeyID" and "ContentKey" attributes. I have tried the following below with no success, I got "Sequence contains no elements" error:

string str = Utility.ReadTextFromUrl(ConfigurationManager.AppSettings["SoapUrl"]);
XElement xdoc = XElement.Parse(str);
string result = xdoc.Descendants("EncryptionInfoResponse")
                    .Descendants("KeyID")                       
                    .First()
                    .Value;
return result;

How do I do this?

---- Edit --------------

I figured out that the problem will be the string from the URL which is a PHP script sending request to a soap service. So I wrote a Soap request with C# and was able to get response body of the soap:

using (WebResponse webResponse = webRequest.EndGetResponse(asyncResult))
{
        using (StreamReader rd = new StreamReader(webResponse.GetResponseStream()))
        {
                soapResult = rd.ReadToEnd();
        }
        System.Diagnostics.Debug.WriteLine(soapResult);
        XDocument xDoc = XDocument.Load(new StringReader(soapResult));

      var unwrappedResponse = xDoc.Descendants((XNamespace)"http://schemas.xmlsoap.org/soap/envelope/" + "Body")
                    .First()
                    .FirstNode;
       System.Diagnostics.Debug.WriteLine(unwrappedResponse);

}

But I got stuck here, I have not been able to read the KeyID and ContentKey nodes, this is the response body:

<RequestEncryptionInfoResponse xmlns="http://tempuri.org/">
  <RequestEncryptionInfoResult>&lt;EncryptionInfoResponse&gt;
  &lt;Status&gt;0&lt;/Status&gt;
  &lt;Message&gt;&lt;/Message&gt;
  &lt;ServiceID&gt;xxxx-xxxx-xxx-xxx&lt;/ServiceID&gt;
  &lt;KeyID&gt;xxxx-xxxx-xxx-xxx&lt;/KeyID&gt;
  &lt;ContentKey&gt;KXnH9nzdDbW6kIw11yvY8A==&lt;/ContentKey&gt;
  &lt;LicAcqURL&gt;&lt;![CDATA[http://sldrm.licensekeyserver.com/core/rightsmanager.asmx]]&gt;&lt;/LicAcqURL&gt;
  &lt;LicUIURL&gt;&lt;/LicUIURL&gt;
  &lt;CustomXML&gt;&lt;![CDATA[&lt;CID&gt;RMgchjQPQS+zfHTzsPGSsQ==&lt;/CID&gt;&lt;DRMTYPE&gt;smooth&lt;/DRMTYPE&gt;]]&gt;&lt;/CustomXML&gt;
  &lt;ContentID&gt;861cc844-0f34-2f41-b37c-74f3b0f192b1&lt;/ContentID&gt;
  &lt;PRHeader&gt;&lt;![CDATA[&lt;WRMHEADER xmlns="http://schemas.microsoft.com/DRM/2007/03/PlayReadyHeader" version="4.0.0.0"&gt;&lt;DATA&gt;&lt;PROTECTINFO&gt;&lt;KEYLEN&gt;16&lt;/KEYLEN&gt;&lt;ALGID&gt;AESCTR&lt;/ALGID&gt;&lt;/PROTECTINFO&gt;&lt;KID&gt;ZEjIHDgPQI+zffOw8ZJ0sQ==&lt;/KID&gt;&lt;LA_URL&gt;http://sldrm.licensekeyserver.com/core/rightsmanager.asmx&lt;/LA_URL&gt;&lt;DS_ID&gt;VlR7IdsIJEuRd06Laqs2jw==&lt;/DS_ID&gt;&lt;CUSTOMATTRIBUTES xmlns=""&gt;&lt;CID&gt;RMgchjQPQS+zfHTzsPGSsQ==&lt;/CID&gt;&lt;DRMTYPE&gt;smooth&lt;/DRMTYPE&gt;&lt;/CUSTOMATTRIBUTES&gt;&lt;CHECKSUM&gt;/ytWga+hG9o=&lt;/CHECKSUM&gt;&lt;/DATA&gt;&lt;/WRMHEADER&gt;]]&gt;&lt;/PRHeader&gt;
&lt;/EncryptionInfoResponse&gt;</RequestEncryptionInfoResult>
</RequestEncryptionInfoResponse>

any help?