What to do when efile flags as invalid because NJ w2 box 19 has amt for local tax withheld, but box 18 is blank, box 20 says FLI? I live & work in NJ, one job, one w2.

Go back to the W2 screen and put the amount in Box 19 into box 14.  Use the drop-down box to select NJ FLI, and then delete your Box 19 entry.  This will remove the diagnostic and allow you to e-file.

Thank you SO much Turbo TaxDanielV!!  This was most helpful.  

You are welcome.

Is this still the case for 2020?  I have AL local income tax in my box 19, but it is telling me box 19 is invalid for efiling. I have never had this issue before. My box 18 has always been blank. Please help. 

Will the IRS have a problem that the Turbo Tax W2 box 14/19 don't match the the W2 sent to IRS by my employer?  I don't want an audit  Thanks

No, the IRS actually does not check boxes 15 though 20 on your W-2 because they are for state and local use. Daniel gave you a workaround for TurboTax's e-file process, which should be OK for you.