You don't indicate what the error messages are, but Tree objects include code references. In order to serialize them with Storable, you either need to have a recent version of Storable (after 2.05) and set $Storable::Deparse to a true value, to allow Storable to serialize the code reference, or prevent the code references from being serialized (see STORABLE_freeze and STORABLE_thaw in Storable).