That's not line 11 of Form 1040. It's line 11 of the Deferral Smart Worksheet for Schedule 3 line 12e. To get rid of the error, don't enter anything on line 11. When the error comes up, delete the zero (or whatever is there) and leave the box empty.
If line 10 of the Smart Worksheet is negative, you are not eligible to defer any of the Social Security portion of the self-employment tax.
