Because the pension plan administrator issued you the incorrect form. They should have issued you a 1099-R, not a 1099-MISC. First, you need to delete the 1099-MISC as entered, and if necessary delete the SCH C. Only after you've done this, should you enter the 1099-MISC per the guidance in the answer box below.
To delete the SCH C, under the Personal Income tab scroll down to Business Items and elect to start/update Business Income & Expenses (SCH C). If you see anything listed there with a Delete button next to it, click that Delete button, then YES to confirm the deletion. That takes care of getting rid of the SCH C.
