How do I fix a "Request format is unrecognized for URL..." error in a web service running in IIS?

Question

Since HTTP GET and HTTP POST are disabled by default try adding the following to your config file:

<configuration>
    <system.web>
    <webServices>
        <protocols>
            <add name="HttpGet"/>
            <add name="HttpPost"/>
        </protocols>
    </webServices>
    </system.web>
</configuration>

I've got the same issue. To solve it add [ScriptService] to your service

    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Web;
    using System.Web.Script.Services;
    using System.Web.Services;

    namespace DemosAjaxcontroltoolkit
    {
        /// <summary>
        /// Summary description for WebService
        /// </summary>
        [ScriptService] 
        [WebService(Namespace = "http://tempuri.org/")]
        [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
        [System.ComponentModel.ToolboxItem(false)]
        // To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line. 
        // [System.Web.Script.Services.ScriptService]
        public class WebService : System.Web.Services.WebService
        {

            [System.Web.Script.Services.ScriptMethod()]
            [WebMethod]

            public string[] GetWords(string prefixText, int count)
            {
                List<string> words = new List<string>();
                words.Add("Apple");
                words.Add("Appertizer");
                words.Add("Apple tree");
                words.Add("Apple Cider");
                words.Add("Afternoon");
                words.Add("Morning");
                words.Add("Breakfeast");
                words.Add("Lunch");
                words.Add("Spider");
                words.Add("Morning");
                words.Add("Day");
                words.Add("Travel");
                words.Add("Night");
                words.Add("Car");
                words.Add("Bikes");
                words.Add("Love");
                words.Add("Good");

                //return words.Where(w => w.StartsWith(prefixText)).Take(count).ToList();

                //List<string> returnedList = words.Where(w => w.StartsWith(prefixText)).Take(count).ToList();
                return words.Where(w => w.ToUpper().StartsWith(prefixText.ToUpper())).ToArray();
            }

        }
    }
}

Just out of interest (- in the case of accessing the web-service via AJAX); I've found that if a 'content-type' header is not passed (- even if it's a local/"HttpPostLocalhost" request), then the issue occurs, so I pass the header myself (- e.g. via jQuery's '$.ajax()' method rather than without via jQuery's '$.getJSON()' method), instead of resorting to this:

https://support.microsoft.com/en-us/kb/819267