If your employer is in Washington state and you did not have any state taxes withheld from your wages in box 17 of the W-2 then you leave boxes 15, 16 and 17 blank.
Washington state does not have a personal income tax.
Turbo tax please correct the program for Washington state box 15. My employer put WA in the first part. I tried several options but what I ended up having to do was to put in WA in box 15 and WA in for the Employer state ID number as well. It would not let me move on unless I did. I tried the app and the web version still the same. Please fix this bug.
If you are receiving an error for box 15 on your Form W-2, and there are no entries in 17, you may leave the entire box 15 and 16 blanks, as well.
If you have entries in box 17, try using the federal ID in box 15, or if the state requires a particular format, such as ending in XYZ, then enter 9999999XYZ for the number of digits it specifies.
Your state department of revenue will be able to easily identify your employer from the 9-digit federal EIN. Hence, the state ID number is redundant anyway but is it still a way that your state tracks employers in their internal state computer system. The state employer ID number is a bureaucratic convenience for your state's department of revenue; it is not an essential element to the correct filing and processing of a valid personal income tax return (either state or federal)
If the error persists, try deleting the form and reentering it. If you have "copied and pasted" to enter some of the information, it might have spaces or other invisible formatting characters causing the errors. Please be sure there are no extra spaces before or after the entries. If you have imported into Turbo Tax, perhaps some of the data was damaged in the transfer and is not working correctly, even if it looks correct on the page. Deleting the W-2 and manually entering it should solve the problem.