asp ToolkitScriptManager and asp ScriptManager for Content Page

Hi,

I am using ajax Rating tool and encountering an error: "AjaxControlToolkit requires ASP.NET Ajax 4.0 scripts". I have found a solution to use ToolkitScriptManager to handle it. Was able to get it work in an independent Web page for testing purpose.

<asp:ToolkitScriptManager ID="toolkitScriptMaster" runat="server">
</asp:ToolkitScriptManager>

When I come back to my website, the ScriptManager on master page has conflict with ToolkitScriptManager on my content page.

"{"Only one instance of a ScriptManager can be added to the page."}

Obviousely, my master page does not accept ToolkitScriptManager to include all javascript libraries, only ScriptManager. I am using Visual Web Developer Express 2013 - Framework 4.5. I have tried AjaxControlToolKit 4.5 and 4.0, both gave me the same error.  Could any one give me a solution?

Thank you in advance,

Ella