NE vs TurboTax Social Security income

Hard to know for sure, since we cannot see what you filed...but:

1) IF you mail-filed, you were supposed to send in a copy of the main Federal 1040 page , that showed the $4876 on line 5b of that form.  IF you did mail file and forget to include it...read their letter closely and send it to the appropriate persons or department that is asking for it as proof (page 1 and 2 of the Federal 1040 will print on one side of one full sheet,  or call NE on Monday and ask what to do.)

or

2)   Was your income on line 5 of the NE form N1040 greater than the limits?  IF so, perhaps NE is correct.   BUT... IF they administratively increased your line 5 NE income with some other income you didn't enter properly, then maybe that pushed line 5 over the income limits that would have allowed you to take the SS deduction.  The NE instructions for line 26 of the Schedule I, show what the income limits are set at.  IF line 5 of the N1040 is over those limits, then the SS deduction is not allowed:

___________

"Line 26 Social Security Income. If line 5 of Form 1040N is $58,000 or less for a married, filing jointly return,
or $43,000 or less for all other filing statuses, enter the amount of Social Security income included in
federal AGI. The amount claimed cannot exceed the amount shown on line 5b, Federal Form 1040,
page 2. Paper filers must attach a copy of pages 1 and 2 of Federal Form 1040 to your Nebraska return."