title: There was an error while trying to serialize parameter http://tempuri.org/:callback
body: <p>I have an asynchronous WCF server (I've derived my own clientbase class) and I call this from my client application.</p>
  
  <p>However, when this method is called:</p>
  
  <pre><code>public IAsyncResult Beginxxx(string path, AsyncCallback callback, object state)  
  {
      return Channel.Beginxxx(path, callback, state); 
  }
  </code></pre>
  
  <p>I get this exception:</p>
  
  <blockquote>
    <p>{"There was an error while trying to serialize parameter <a href="http://tempuri.org/:callback" rel="nofollow">http://tempuri.org/:callback</a>. The InnerException message was 'Type 'System.DelegateSerializationHolder+DelegateEntry' with data contract name 'DelegateSerializationHolder.DelegateEntry:http://schemas.datacontract.org/2004/07/System' is not expected. Add any types not known statically to the list of known types - for example, by using the KnownTypeAttribute attribute or by adding them to the list of known types passed to DataContractSerializer.'.  Please see InnerException for more details."}</p>
  </blockquote>
  
  <p>If I had my own class with its own properties, this exception would make sense but this is a standard .NET type (AsyncCallback I believe the exception is complaining about). A code sample of what I am trying to do doesn't have this problem (and I changed that to the same type of binding I am using - named pipes).</p>
  
  <p>What is wrong?</p>