无法从ajax获取数组

I have asp.net application where need to implement autocomplete, I try to load list of names from server side and then deserealize it in js code, but have an 500 error, can anybody help me?

Unknown web method GetListofCompanies.
Parameter name: methodName

Code:

[WebMethod]
    [ScriptMethod(ResponseFormat = ResponseFormat.Json)]
    public string GetListofCompanies(string name) {
        var companies = _companyRepo.GetAll().Select(x => x.Name).ToList();

        // Create a JSON object to create the response in the format needed.
        JavaScriptSerializer oJss = new JavaScriptSerializer();

        // Create the JSON response.
        String strResponse = oJss.Serialize(companies);

        return strResponse;

    }

JS:

var name = "";
        $.ajax({
            url: "Company.aspx/GetListofCompanies",
            type: "post",
            data: { name: name },
            dataType: "json",
            contentType: 'application/json',
            success: function (data) {
                // Get the data.
                var responseArray = JSON.parse(data.d);
                $("#txtName").autocomplete({
                    source: responseArray
                });
            }
        });

// Namespaces.
using System.Web.Services;
using System.Web.Script.Serialization;   

[WebMethod]
public static string GetListofCompanies(string name)
{
    List<string> companies = new List<string>();
    companies.Add("Company1");
    companies.Add("Company2");
    companies.Add("Company3");
    companies.Add("Company4");
    companies.Add("Company5");

    // Create a JSON object to create the response in the format needed.
    JavaScriptSerializer oJss = new JavaScriptSerializer();

    // Create the JSON response.
    String strResponse = oJss.Serialize(companies);

    return strResponse;
}

   // JS
   function request() {
        var name = "";
        var data = { name: name };
        $.ajax({
            url: "Default.aspx/GetListofCompanies",
            type: "POST",
            contentType: 'application/json',
            data: JSON.stringify(data)
        }).success(function (data) {
            // do your stuff here
        })
        .fail(function (e) {
            alert("Error");
        });
    }