Unless you have a local tax where you live (very rare) and there is an amount withheld in box 19 then all boxes 18-20 must be blank.
You can try entering 0 in Box 20, to see if that helps to resolve this issue. Box 20 and Box 19 go together.
Box 19: Local income tax — The amount of tax withheld for the locality in Box 20. This amount is entered on the appropriate line of your local return.
Box 20: Locality name — The description of the place — like a city or town — for which taxes were also withheld.
If both Box 19 and 20 are empty just do not enter any information in TurboTax for these fields.
If you have an amount in box 19, but nothing in box 20, this is a problem. With an amount in box 19, box 20 needs a locality name that the amount in box 19 was paid to. This is usually a city income tax or sometimes state disability payments. In any case, there needs to be a locality name in box 20, if box 19 includes any amount.
If you do have an amount in box 19 then you need to contact your employer and ask they correct the W2 before you file.