Wrong. Accirding to the Form 6781 instruction -
The amount you can carry back to any prior year is limited to the smaller of:
• The gain, if any, that you would report on line 16 of Schedule D (Form 1040) for that carryback year if only gains and losses from section 1256 contracts were taken into account;
OR
• The gain, if any, reported on line 16 of Schedule D (Form 1040) for that carryback year.
So if the carryback year line 16 of Schedule D is positive, you can.
