ora-00942 or ora-12003 when attempting to drop a materialized view

We have a couple of materialized views that can't be dropped. They exist and can be queried, but can't be dropped. This seems similar to the issue in article ID 1072858.1, but as shown here, both the table and mview objects appear (but with the mview marked as invalid):

SQL> select o.OBJECT_NAME, o.OBJECT_ID, o.OBJECT_TYPE, o.status
  2  from all_objects o
  3  where o.OBJECT_NAME = 'UCDR_PMATS_VL2';

OBJECT_NAME                     OBJECT_ID OBJECT_TYPE         STATUS
------------------------------ ---------- ------------------- -------
UCDR_PMATS_VL2                     172787 TABLE               VALID
UCDR_PMATS_VL2                     172788 MATERIALIZED VIEW   INVALID

I've logged in as sysdba and tried dropping it there as well as tried to drop the summary as described in the article. Nothing seems to work. Any ideas?