Web Services and CF

Hello, I've just started using Coldfusion and I'm trying to invoke a Web Service:

<cfinvoke
webservice=" http://localhost/WebService1/Service1.asmx?wsdl"
method="MyMethod"
returnvariable="aString">
<cfinvokeargument name="arg1" value="1"/>
<cfinvokeargument name="arg2" value="2"/>
<cfinvokeargument name="arg3" value="3"/>
</cfinvoke>

But I get the following error:
Web service operation MyMethod with parameters {arg1={1},arg2={2},arg3={3}} cannot be found.

This is my web service method in C# .Net:
public String MyMethod(string arg1, string arg2, string arg3)
{
return "Hello World";
}

I've tried with a very similar method which just have 2 parameters (arg1, arg2) instead of 3 and it works.

Could anyone help me?

Thanks