Box 15, Employer's State ID, what do I enter if it's blank? State of Texas. Turbo Tax clearly says to leave blank f blank, but then keeps telling me there is an issue.

[Hal_Al]

If there are entries in boxes 16 -20 of your W-2, or the state ID box, delete them. Any such entries must have an state identified in box 15.  Since TX has no income tax, there is no need for there to be anything in those boxes, unless you also worked in a state other than TX.