Request format is unrecognized

[Merighi]

I've this problem: i'm trying to build a method that outputs an object like this:

public class Autenticazione
{

public string Username
{
set
{
Username=value;
}

get
{
return Username;
}

}

public string Password
{
set
{
Password=value;
}

get
{
return Password;
}

}

The WebService implementation is this:

public class Service1 : System.Web.Serv ices.WebService
{
public static Autenticazione aut;
public Service1()
{
InitializeCompo nent();
aut = new Autenticazione( );
aut.Username="u sername di prova";
aut.Password="p assword di prova";
}
[WebMethod]
public Autenticazione get_Autenticazi one()
{
return aut;

}

When i try to call the method, i receive this response:
Request format is unrecognized.

Is there anyone who can help me?

Thanks

Francesca