ajax and webservices...

I have created a dataset. Each method of the tableadapter shows the right data when I preview it at design time.
However, when I load the page I get the value in both dropdownlists: [method error 500]

If I step throught the code, the webmethod is not hit even though I put a breakpoint on it (or is that normal?)

Here's my code:

.ASPX

<asp:DropDownList ID="ddlCountry1" runat="server">
</asp:DropDownList>
<asp:DropDownList ID="ddlLocalCity" runat="server">
</asp:DropDownList>

<cc1:CascadingDropDown ID="CascadingDropDown1"
runat="server"
TargetControlID="ddlCountry1"
Category="CountryName"
prompttext="Select country"
ServicePath="LocalCities.asmx"
ServiceMethod="GetCountries">
</cc1:CascadingDropDown>
<cc1:CascadingDropDown ID="CascadingDropDown2"
runat="server"
TargetControlID="ddlLocalCity"
Category="CityName"
prompttext="Select city"
ServicePath="LocalCities.asmx"
ServiceMethod="GetCitiesForCountry"
LoadingText="Loading...">
</cc1:CascadingDropDown>

Local.vb

<WebMethod()> _
Public Function GetCountries(ByVal knownCategoryValues As String, ByVal category As String) As CascadingDropDownNameValue()
Dim countryAdapter As CountryMainCitiesTableAdapters.CountriesTableAdapter = New CountryMainCitiesTableAdapters.CountriesTableAdapter
Dim countries As CountryMainCities.tblCountriesDataTable = countryAdapter.GetData
Dim values As New List(Of CascadingDropDownNameValue)
For Each dr As DataRow In countries
Dim CountryName As String = CType(dr("CountryName"), String)
Dim countryId As Integer = CType(dr("CountryID"), Integer)
values.Add(New CascadingDropDownNameValue(CountryName, countryId.ToString))
Next
Return values.ToArray
End Function

<WebMethod()> _
Public Function GetCitiesForCountry(ByVal knownCategoryValues As String, ByVal category As String) As CascadingDropDownNameValue()
Dim kv As StringDictionary = CascadingDropDown.ParseKnownCategoryValuesString(knownCategoryValues)
Dim countryId As Integer
If (Not kv.ContainsKey("CountryID") _
OrElse Not Int32.TryParse(kv("CountryID"), countryId)) Then
Return Nothing
End If
Dim cityAdapter As New DataTable

Dim adapter As CountryMainCitiesTableAdapters.CountryMainCitiesTableAdapter = New CountryMainCitiesTableAdapters.CountryMainCitiesTableAdapter
Dim cityTable As CountryMainCities.tblCountryMainCitiesDataTable = adapter.GetDataByCountryID(countryId)
Dim values As New List(Of CascadingDropDownNameValue)
For Each dr As DataRow In cityTable
values.Add(New CascadingDropDownNameValue(CType(dr("CityName"), String), dr("CityID").ToString))
Next
Return values.ToArray
End Function

Try to follow up the following suggestions to fix the famous Method Error 500 for reference.
1.Try to read this thread -http://forums.asp.net/1476672/ShowThread.aspx#1476672
2.Try to write a web method in behind code to call web service as the following
???Country:<asp:DropDownList ID="ddlCountry" runat="server">
???</asp:DropDownList>
???<AjaxControls:CascadingDropDown ID="CascadingDropDown1" runat="server" TargetControlID="ddlCountry" Category="Country" ????LoadingText="Loading....." ServiceMethod="GetCountries" BehaviorID="CascadingDropDown1" PromptText="- select country -">
???</AjaxControls:CascadingDropDown
???[WebMethod]
???[ScriptMethod]
???public CascadingDropDownNameValue[] GetCountries()
???{
???????WebService ws = new WebService();
???????return ws.GetCountries();
???}
Wish the above can help you.

The other thread did not help me a lot. But I changed some code, however I still receive the error [method 500]

and if I add the attribute
ServicePath="default.aspx.vb" to CascadingDropDown2 I receive the error [method 404]

The code-behind method GetCitiesForCountry is never hit...

DEFAULT.ASPX

<asp:DropDownList ID="ddlCountry1" runat="server">
</asp:DropDownList>
<asp:DropDownList ID="ddlLocalCity" runat="server">
</asp:DropDownList>

<cc1:CascadingDropDown ID="CascadingDropDown1"
runat="server"
TargetControlID="ddlCountry1"
Category="CountryID"
prompttext="Select country"
ServicePath="LocalCities.asmx"
ServiceMethod="GetCountries">
</cc1:CascadingDropDown>
<cc1:CascadingDropDown ID="CascadingDropDown2"
runat="server"
TargetControlID="ddlLocalCity"
ParentControlID="ddlCountry1"
Category="CityID"
prompttext="Select city"
ServicePath="default.aspx.vb"
ServiceMethod="GetCitiesForCountry"
LoadingText="Loading...">
</cc1:CascadingDropDown>

DEFAULT.ASPX.VB

<WebMethod(), Microsoft.Web.Script.Services.ScriptMethod()> _
Public Function GetCitiesForCountry(ByVal knownCategoryValues As String, ByVal category As String) As CascadingDropDownNameValue()
Dim kv As StringDictionary = CascadingDropDown.ParseKnownCategoryValuesString(knownCategoryValues)
Dim CountryID As Integer
If (Not kv.ContainsKey("CountryID") _
OrElse Not Int32.TryParse(kv("CountryID"), CountryID)) Then
GlobalFunctions.ReportError("CountryID: ", "WHOOPS")
Return Nothing
End If
GlobalFunctions.ReportError("CountryID: ", CountryID.ToString)
Dim cityadapter As CountryMainCitiesTableAdapters.CountryMainCitiesTableAdapter = New CountryMainCitiesTableAdapters.CountryMainCitiesTableAdapter
Dim cities As CountryMainCities.tblCountryMainCitiesDataTable = cityadapter.GetDataByCountryID(CountryID)
Dim values As New List(Of CascadingDropDownNameValue)
For Each dr As DataRow In cities
GlobalFunctions.ReportError("CityID: ", dr("CityID").ToString)
values.Add(New CascadingDropDownNameValue(CType(dr("CityName"), String), dr("CityID").ToString))
Next
Return values.ToArray
End Function