As you work with web services in ASP.NET, it is likely that you will eventually come upon a weird file not found exception. The actual text of the exception will look something like “File or assembly name jdiw83ls.dll, or one of its dependencies, was not found". Now, since it unlikely that you have a project with a name of jdiw84ls in your solution, the source of this exception and it's resolution will be hard to see.
To understand where the message is coming from requires a little detail about how ASP.NET services moves complex objects across its boundary. If you pass a complex object to a web service, the client side serializes the class into an XML document. On the receiving side (the server), the inbound XML document is deserialized back into a class. This knowledge is part of Web Services 101.
However, what happens when the class
<add name="XmlSerialization.Compilation" value="4"/>