A UA 764 has 8 rows of BF. In front of row 1 are exit doors 1L and 1R. Just behind row 8 is the second bank of exit doors 2L and 2R. I assume the decision to close rows 1-4 was because exit door bank 1 would have been the closest doors to these rows, and because 1R was inoperative, they could not be relied upon. Bank 2 would be the closest doors to rows 5-8.

See http://www.seatguru.com/airlines/Uni...767_400_ER.php