Aflac post-tax, paid 100% by emloyee is showing up on the w-2 as a negative in box 14. What is the correct way to have this set up and how do I correct it?

AFLAC is a supplemental insurance, NFD17. Let me guide you with setting it up.

First, let's edit the payroll item. Here's how:

1. Click Lists, then go to Payroll Item List.
2. Select the item, then double-click to open the setup window.
3. Continue clicking Next until the Tax tracking type window.
4. Select the tax tracking type. I'd suggest conferring with your accountant on the best way to categorize it. 
5. Continue clicking Next until the Gross vs. net window, then select Net pay.
6. Click Next, then Finish. 

When you create a paycheck, the payroll item will be deducted from the net pay. 

I'll include an article about setting up a payroll item for an insurance for future reference. 

We'll be right here if you have other payroll concerns.