Cannot process the message because the content type 'text/xml; charset=utf-8' was not the expected type 'application/soap+xml; charset=utf-8'

'text/xml' is the content type for SOAP 1.1 while 'application/soap+xml' is the content type for SOAP 1.2 and your client WCF 3.0 use SOAP 1.1 while the service with WCF 3.5 use SOAP 1.2.

Here is the solution that worked for me. If you have access to the service config, you just have to change the binding to use SOAP 1.1 :

Add a new custom binding in the 'bindings' section

      <customBinding>
        <binding name="Soap11HttpBinding">
          <textMessageEncoding messageVersion="Soap11" />
          <httpTransport />
        </binding>
      </customBinding>

and don't forget to update your endpoint with the new binding :

    <endpoint ...
        binding="customBinding"
        bindingConfiguration="Soap11HttpBinding">
        ...
    </endpoint>

• [Bad] do a lot's of replace like

inputString = inputString.Replace('À', 'A');

repeat for ÀÁÂÃÄâãäàáÈÉÊËêëèéÌÍÎÏîïìíÒÓÔÖôõöòóÙÚÛÜûüùúÝýÑñç and maybe miss some exotic chars or the Õ in this list !

• [Good] or you can use this function

	public static string RemoveDiacritics(string inputString)
	{
		//!\\ Warning 'œ' will be replaced with a 'o' not an 'oe'
		String normalizedString = inputString.Normalize(NormalizationForm.FormD);
		StringBuilder stringBuilder = new StringBuilder();
		for (int i = 0; i < normalizedString.Length; i++)
		{
			Char c = normalizedString[i];
			if (System.Globalization.CharUnicodeInfo.GetUnicodeCategory(c) != System.Globalization.UnicodeCategory.NonSpacingMark)
				stringBuilder.Append(c);
		}
		return stringBuilder.ToString();
	}

Hopefully this page from Ibm explain the different style/use in SOAP message.

A WSDL document describes a Web service. A WSDL binding describes how the service is bound to a messaging protocol, particularly the SOAP messaging protocol. A WSDL SOAP binding can be either a Remote Procedure Call (RPC) style binding or a document style binding. A SOAP binding can also have an encoded use or a literal use.

Ok now I know that four style/use models:
RPC/Encoded, RPC/literal, Document/encoded or Document/literal

But how do I do that in WCF C# ?? It's very easy, just use the [XmlSerializerFormat] attribute.

Here is a very very simple test to check the different result in the soap message:

Interface of the Wcf service used :

using System.ServiceModel;

namespace WcfService1
{
    [ServiceContract]
    public interface IService1
    {
        [OperationContract]
        [XmlSerializerFormat(Style = OperationFormatStyle.Rpc, Use = OperationFormatUse.Encoded)]
        string TestRpcEncoded(int value);

        [OperationContract]
        [XmlSerializerFormat(Style = OperationFormatStyle.Rpc, Use = OperationFormatUse.Literal)]
        string TestRpcLiteral(int value);

        //[OperationContract]
        //[XmlSerializerFormat(Style = OperationFormatStyle.Document, Use = OperationFormatUse.Encoded)]
        //string TestDocumentEncoded(int value);

        [OperationContract]
        [XmlSerializerFormat(Style = OperationFormatStyle.Document, Use = OperationFormatUse.Literal)]
        string TestDocumentLiteral(int value);
    }
}

Result captured on the network with fiddler:

For clarity, I have removed:

RPC / Encoded call

<!-- Request -->
<s:Body s:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">
  <q1:TestRpcEncoded>
    <value xsi:type="xsd:int">42</value>
  </q1:TestRpcEncoded>
</s:Body>

<!-- Response -->
<s:Body s:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">
  <q1:TestRpcEncodedResponse>
    <TestRpcEncodedResult xsi:type="xsd:string">You entered: 42</TestRpcEncodedResult>
  </q1:TestRpcEncodedResponse>
</s:Body>

RPC / Literal call

<!-- Request -->
<s:Body>
  <TestRpcLiteral>
    <value xmlns="">42</value>
  </TestRpcLiteral>
</s:Body>

<!-- Response -->
<s:Body>
  <TestRpcLiteralResponse>
    <TestRpcLiteralResult xmlns="">You entered: 42</TestRpcLiteralResult>
  </TestRpcLiteralResponse>
</s:Body>

Document / Encoded call
If you add the TestDocumentEncoded you will get an InvalidOperationException.
This combination is not supported.

Document / Literal call

<!-- Request -->
<s:Body></code>
  <TestDocumentLiteral><value>42</value></TestDocumentLiteral>
</s:Body>

<!-- Response -->
<s:Body>
  <TestDocumentLiteralResponse>
    <TestDocumentLiteralResult>You entered: 42</TestDocumentLiteralResult>
  </TestDocumentLiteralResponse>
</s:Body>

is a common mystake if you want to transmit to someone or to be sure that you have something like "HH:mm:ss" because the character (:) is not just a colon, it's a time separator wich depend on the locale.

Here is a list of culture where the (:) change into a dot (.)
it-IT : Italian (Italy)
fo-FO : Faroese (Faroe Islands)
bn-BD : Bengali (Bangladesh)
ml-IN : Malayalam (India)
bn-IN : Bengali (India)

To workaround you can use CultureInfo.InvariantCulture or escape the colon character.

... and same story for the date separator "/" but this one is at this time the same for every culture.

You can follow the instruction on the steam support page or you can use my little tool and if you don't trust me the source code is available.

Have fun !
Whaly

XmlWriter writer = new XmlTextWriter(stream, Encoding.UTF8);

But the output contains an UTF header, the Byte Order Mark (BOM). The use of the header/signature is usually for xml file, if you want to use the ouput in an HttpResponse, you don't need the signature. (some parser can cause a parsing error in java, like org.xml.sax.SAXException).

Here is the change to remove the BOM :

XmlWriter writer = new XmlTextWriter(stream, new UTF8Encoding(false));