Why is MicrosoftAjax.en-US.js expected when MicrosoftAjax.js specified

Even though in my test page the MicrosoftAjax.js is included in the path, it returns an error saying "Sys" is undefined"... View source of the page shows that somehow MicrosoftAjax.en-US.js  is in the path.

<asp:ScriptManager ID="ScriptManager1" runat="server"  >
            <asp:ScriptReference Name="MicrosoftAjax.js" ScriptMode="Auto" Path="MicrosoftAjaxLibrary/System.Web.Extensions/" />
            <asp:ScriptReference Name="MicrosoftAjaxWebForms.js" ScriptMode="Auto" Path="MicrosoftAjaxLibrary/System.Web.Extensions/" />


 I made a copy of  /MicrosoftAjax.js" &  MicrosoftAjaxWebForms.js and called it MicrosoftAjax.en-US.js & MicrosoftAjaxWebForms.en-US.js in the same location and now it works.
I'm not sure why this is and what the ramifications are if I move this to production.  Any suggestions?
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nicholsfAuthor Commented:
Setting  EnableScriptLocalization="false"  in the ScriptManager Tag fixed the problem
<asp:ScriptManager ID="ScriptManager1" runat="server" EnableScriptLocalization="false" >

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