Passing an object of type System.Text.Encoding to a Web Service is
problematic because the proxy will contain a copy of that type. The copy is
an abstract class with no properties and is pretty much useless. To see
this, take a look at the proxy code in reference.cs.

Now you can actually pass objects of type System.Text.Encoding to a Web
Service if you add XmlInclude attributes to the web method. However this
would be a bit unpractical as you would have to list all Encoding types
you're expecting like so:

[WebMethod]
[XmlInclude(typeof(System.Text.UnicodeEncoding))]
[XmlInclude(typeof(System.Text.AsciiEncoding))]
// etc...
public bool MyWebFunc(string encodingName)
{
   ...
}

You would also have to modify the generated proxy accordingly, which in
general is a bad idea as the modifications are lost as soon as you
regenerate the proxy.

An easy work-around to the problem is to use a simple string parameter like
so:

[WebMethod]
public bool MyWebFunc(string encodingName)
{
   try
   {
       System.Text.Encoding enc =
System.Text.Encoding.GetEncoding(encodingName);
   }
   catch (Exception ex)
   {
       // not a valid encoding...
       throw ex;
   }
}

hth,
Sami