6027   Invalid master index

   Problem:   A tag that already existed in a CDX was being reindexed using
   a master index, but the master index was the tag being reindexed.

   Solution:  If reindexing an existing tag such that a master index is
   involved (e.g. the tag is a subindex), make sure the active index order
   is not set to the index that is to be reindexed.