Try this from the migration guide:

In the Web.config file, add the following entry in the <httpHandlers> element for the new ScriptResourceHandler object in Beta 2:

<add verb="GET"

  path="ScriptResource.axd"

  type="Microsoft.Web.Handlers.ScriptResourceHandler"

  validate="false"/>

The release notes state the following:

This handler requires an entry in the web.config file.  If the entry is missing, you might see the following error:

    'Sys' is undefine.

I hope this helps!