Modalpopup - Web Service Call Failed

My web service works great when I call it outside of the modalpopupextender. However, I can't seem to access the asmx page at all when using the modalpopup dynamic properties. I keep receiving errors stating both "web service call failed: 12030" & "web service call failed: 500" randomly. What am I missing here? Any help you can lend to my problem would be greatly appreciated!

<ajaxToolkit:ToolkitScriptManagerID="ScriptManager1"runat="server">
<Services>
<asp:ServiceReferencepath="~/GetCity.asmx"/>
</Services>
</ajaxToolkit:ToolkitScriptManager>

<asp:GridViewID="GridView1"runat="server"DataKeyNames="FILENAME"AutoGenerateSelectButton="True">
<Columns>
<asp:TemplateField>
<ItemTemplate>
<asp:linkButtonID="hlnkOrders"runat="server">Selectlnk</asp:linkButton>
<ajaxToolkit:ModalPopupExtenderID="ModalPopupExtender3"runat="server"
OKControlID="btnOK"
PopupControlID="Panel3"
TargetControlID="hlnkOrders"
DynamicServicePath="GetCity.asmx"
DynamicServiceMethod="LookupCityCode"
DynamicControlID="lblhidden"
DynamicContextKey='<%=eval("FILENAME") %>'
BackgroundCssClass="modal"
DropShadow="true">
</ajaxToolkit:ModalPopupExtender>
</ItemTemplate>
</asp:TemplateField>
</Columns>
<AlternatingRowStyleBackColor="#FFFFC0"BorderColor="#004000"BorderWidth="1px"/>
</asp:GridView>

<asp:Panelrunat="server"ID="Panel3"BackColor="AliceBlue">
<asp:LabelID="lblHidden"runat="server"></asp:Label><br/><br/>
<asp:Buttonrunat="server"ID="btnOK"Text="OK"/>
</asp:Panel>

Imports System.Web.Script.Services.ScriptServiceAttribute
Imports System.Web.Script.Services.ScriptMethodAttribute

<WebService(Namespace:="http://tempuri.org/")> _
<WebServiceBinding(ConformsTo:=WsiProfiles.BasicProfile1_1)> _
<Global.Microsoft.VisualBasic.CompilerServices.DesignerGenerated()> _
PublicClass GetCity

Inherits System.Web.Services.WebService

Private strUserNameAsString =""
Private strServerNameAsString =""
Private strPasswordAsString =""
Private wAttachmentPathAsString =""

<WebMethod()> _
PublicFunction LookupCityCode(ByVal contextKeyAsString)AsString

'do some stuff
ReadExcelOrder(wattachmentPath & contextKey)
LoadParameters()

End Function

PrivateFunction ReadExcelOrder(ByVal FileNameAsString)AsString

'do some stuff

End Function

PrivateSub LoadParameters()

'do some stuff

End Sub

I'll answer my own question here. Once I added the property System.Web.Script.Services.ScriptService to the webservice, it works!

<WebService(Namespace:="http://tempuri.org/")> _
<System.Web.Script.Services.ScriptService()> _
<WebServiceBinding(ConformsTo:=WsiProfiles.BasicProfile1_1)> _
<Global.Microsoft.VisualBasic.CompilerServices.DesignerGenerated()> _
PublicClass GetCity

Even after adding

[System.Web.Script.Services.ScriptService]

 to my service it is not working. Please help