I need to call server side code "c# Function" in my asp.net project in javascript so i used this way:
<script type="text/javascript">
    function doReadPublicData() {
        PageMethods.btnVerifyPubData_Click(OnGetMessageSuccess, OnGetMessageFailure);
    }
    function OnGetMessageSuccess(result, userContext, methodName) {
        alert(result);
    }
    function OnGetMessageFailure(error, userContext, methodName) {
        alert(error.get_message());
    }
</script>
And I enabled the EnablePageMethods property in the script manager:
<asp:ScriptManager ID="ScriptManager1" EnablePageMethods="true" runat="server">
</asp:ScriptManager>
<asp:Button ID="btnVerifyPubData" runat="server" OnClientClick="doReadPublicData();"
    OnClick="btnVerifyPubData_Click" Text="Show Information"
    CssClass="submitButton" PostBackUrl="~/ParsePublicData.aspx" />
But this error occurs.