After Updating to RC, I got this Error:

 Assembly 'Microsoft.Web.Preview, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' does not contain a Web resource with name 'Microsoft.Web.Preview.Resources.ScriptLibrary.PreviewScript.js'.

Where is PreviewScript.js? ;)

My Reference is:

Thank you!

Adding script references are simpler now:

<asp:ScriptReference Assembly="Microsoft.Web.Preview" Name="PreviewScript.js" />

 Just leave off the Microsoft.Web.Resources.ScriptLibrary 

Slightly more detail on what changed in the December CTP here:

http://weblogs.asp.net/infinitiesloop/archive/2006/12/14/asp-net-2-0-ajax-futures-december-ctp-released.aspx

and here:

http://weblogs.asp.net/infinitiesloop/archive/2006/12/14/ajax-futures-december-ctp-returning-datasets-datatables-and-datarows-from-a-webservice-or-pagemethod.aspx

Thank You JWMCpeak
It really helped me