Call a webservice that returns ISO-8859-1 data

Hello,

From a web forms application I need to call a webservice that returns ISO-8859-1 data. I had an exception so I tried to configure this in the web.config:

<extensions>

<bindingElementExtensions>
<add name="customTextMessageEncoding"
type="Microsoft.ServiceModel.Samples.CustomTextMessageEncodingElement,
Microsoft.ServiceModel.Samples.CustomTextEncoder"/>
</bindingElementExtensions>
</extensions>
<bindings>
<customBinding>
<binding name="ISO8859Binding" >
<customTextMessageEncoding encoding="ISO-8859-1" />
<httpTransport />
</binding>
</customBinding>
</bindings>

<client>
<endpoint address="https://...."
binding="customBinding" bindingConfiguration="ISO8859Binding"
contract="Service" name="AddServicePort" />
</client>

But I have the error:

Could not load type 'Microsoft.ServiceModel.Samples.CustomTextMessageEncodingElement,
Microsoft.ServiceModel.Samples.CustomTextEncoder' registrado para la extensión 'customTextMessageEncoding'.

How Can I find the way to load??

Microsoft.ServiceModel.Samples.CustomTextMessageEncodingElement, 

Microsoft.ServiceModel.Samples.CustomTextEncoder

Thanks in advance.