The RDB$REL_REL_ID_NDX index could not be processed

  Explanation:  The RDB$REL_REL_ID_NDX index must  be  scanned  to
  identify  the  valid  relation  record types.  The index, or the
  RDB$DATABASE relation, or the root file is corrupt.

  User Action:  Locate and correct the corruption with RMU  ALTER,
  and  try  again.   Alternatively,  you  can  use the RMU Restore
  command to restore the database from a backup file.