The state of Nevada is not listed because it is one of the states without a personal income tax. Make sure you leave all state and county boxes empty. Otherwise, you will get errors when trying to submit your return.
In the state of Nevada do I leave the following boxes empty: 13, 14 and 15 even thou 14 has a value on the W-2G?
If your Form W-2G has nothing shown for the state ID number, no state winnings, and no state tax withheld (such as for Nevada), then don't choose anything from the drop-down list of state names and leave the other state fields blank. This should resolve the error. The instructions for Boxes 13-18 indicate "Leave blank if empty on your form". Don't enter zeros if the fields are blank.
If your W-2G is only for Nevada, then yes, you can leave boxes 13, 14, and 15 blank.
Box 13 on Form W-2G is for the State payer ID number. TurboTax also provides a drop-down menu to choose the name of the state, which is actually not shown in box 13, but only in the payer address field.
If you live in a state with income tax, you only need a payer ID number if there was state withholding entered for that state. If not, don't select your state from the drop-down menu and leave the other state boxes blank.
If you entered something in the state section of your W-2G and it's coming up as an error in Review, try deleting the W-2G (click the trash can icon next to the item) and entering it again.
See this TurboTax tips article for more information on Form W-2G.