Did you file a Federal return? You can't e-file your State return. You can only e-file your State using TurboTax if you also e-file your Federal return. Your Federal return must has been accepted to file just a State return. If you filed your Federal return with TurboTax, you can then file just a state returns. On the screen where it asks what returns you want to file, check Do not file Federal.
The TurboTax state program is designed to transfer information from your federal return. For this reason, TurboTax state isn't sold as a standalone tax-preparation product.