At this point, I think you are running into an e-filing issue within TurboTax. An update to fix the issue is expected to be released around 4/5/2019. You can check out this TurboTax FAQ for more information: Excess 401(k) Contribution Preventing E-filing.
Be sure to sign up for updates to be alerted as soon as there is a solution. If you do not want to wait for an update, you have the option to paper file your tax returns as this is only an e-filing issue.
If you haven't done so already, use the steps in this answer to include your excess contribution as wages on your 2018 Tax Return: What
to do if you have an excess contribution to a 401(k).
