Couple of possibilities.
If you filed a "non-filer" form to get your stimulus faster, that counts as a tax return and you can't e-file two tax returns. The IRS is "working on" a fix to allow people in that situation to e-file, but for now, your only option is to print your return and mail it.
You may also get that message if you are a victim of identity theft. Again the only way to file is to print your return and mail it, but you may want to call customer support and ask to talk to the security department first. Use the secure web form to get the appropriate contact number. https://support.turbotax.intuit.com/contact/
