This particular mock up template can only be used with Elements 11 and up.
Since Elements does not have the capability to "replace contents" in a smart object, you will need to load and use a simple action to make the mock up work. You can download the action with easy instructions here:
DOWNLOAD THE ACTION SET FOR ELEMENTS
Simply use the "Replace Image" action on each layer of the mock up instead of "Replace Contents" as mentioned in the mock up instructions.