This index was previously specified with a STORE clause.
  Continue?  [N]

  Explanation:  You are specifying an ALTER INDEX statement
  without a STORE clause, which places the index into the
  RDB$SYSTEM storage area.  The index was previously specified as
  being stored in a different area.  SQL is confirming whether you
  want the index placed in the RDB$SYSTEM storage area.

  User Action:  An affirmative reply (Y or YES) causes the
  operation to continue.  A negative reply (a carriage return, N,
  or NO) terminates the operation.