Using webclient to create asmx or config will cause "The remote server returned an error:(403) Forbidden"

Question

I don't understand why I can't create n test.asmx/test.config file but I could make test.dll or any other file extention using the same codes below:

WebClient webClient = new WebClient();
    string data = "upload data using webclient.";
    Stream stream = webClient.OpenWrite("http://152.226.152.162/rightfolder/test.asmx", "PUT");
    StreamWriter sw = new StreamWriter(stream);
    sw.WriteLine(data);
    sw.Close();
    stream.Close();

Doing this will get me an 403 error unless not .asmx/.config

Is there anything I could do to allow such thing.

The folder in IIS, right folder has Internet Guest Account write permission checked but even without it I could still create a test.dll but not asmx/config.