Data loading but update panel Not updating Due To ScriptManager Error : Asp

**Introduction**

Hi All,

I am updating dropdownlist "SiteName" from another dropdownlist selection "SiteType" asynchronously. Aspx code is shown below.

<asp:ScriptManager ID="ScriptManager1" runat="server" enablepartialrendering="True"/>
Search for a Placemark.<br /><br /><b>Select a Site Type : </b><br /><asp:DropDownList id="SiteType" runat="server" AutoPostBack="true" 
OnSelectedIndexChanged="SiteType_SelectedIndexChanged"></asp:DropDownList><br /><b>Select a Site Name : </b><br /><asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional" ChildrenAsTriggers="true"><ContentTemplate><asp:DropDownList id="SiteName" runat="server" AutoPostBack="false" 
OnSelectedIndexChanged="SiteName_SelectedIndexChanged"></asp:DropDownList></ContentTemplate><Triggers><asp:AsyncPostbackTrigger ControlID="SiteType" EventName="SelectedIndexChanged" /></Triggers></asp:UpdatePanel>I get this error when selecting options from dropdownlist.

> The message received from server could not be parsed.

The important points to note,

1- Data is successfully getting, i can see it in response in dev tool inspect.

2- When i change trigger to PostbackTrigger from AsyncPostbackTrigger, it start working but not partial updating as required.

If someone have any idea please let me know. Thanks for your time.