the instructions you presented say the 11 and 13ZZ should be combined and reported on schedule E line 28. so you can enter 11 and 13 separately and the link each to the form or do a net entry on 11 which would require only 1 linking. in either case the net result should be the same.
the error on the 6781 may be due to the fact that if c/b is elected, the amount of the carryback must be entered on line 6 of the form as a positive number. it can't be left blank but can be any number up to the current year 1256 loss.
