Sign in to TurboTax on a computer with the Chrome browser. Clear all browsing data before signing in. Delete the entire W-2 entry. Then type the W-2 in again manually. Do not try to download it. That should remove the error and let you e-file.
What can I do if TurboTax keeps telling me my employer's state tax id is wrong, and it won't let me e-file?
It says it needs to be 14 characters, and it is.
Since you mentioned "14 characters", I'll go out on a limb and assume you are a UTAH filer and that the error is in regard to the Employer state withholding ID number. There is a known bug that many Utah filers have experienced in that regard. The quirky solution is usually simple, but not intuitive.
The Employer state withholding ID number shown on your W-2 is ultimately reported on the Utah Form TC-40W. A state withholding number can also be on a 1099, if applicable. When entering the Employer/Payer state withholding ID number in TurboTax, it should be 14 characters that end with the letters wth. The solution is to use lower case letters for the wth--not capital letters. Also be sure to enter the 14 characters without any dashes/hyphens.
Note: You must use the lower case wth on all W-2's and any 1099's that have a Utah state Employer/Payer withholding ID number.