Library /sys$common/syshlp/RDOHELP72.HLB  —  Replication Option, RDMS_ERRORS, NODELCACHE
  the default cache RDB$CACHE may not be deleted

  Explanation:  You attempted to drop the default cache RDB$CACHE.
  This is not permitted.

  User Action:  Make sure the cache you drop is  not  the  default
  cache RDB$CACHE.
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