The IRS - not eFile.com - has rejected your return and you are required to make a correction.
Solution: Please sign in to your eFile.com account now and click on My Return in the upper left and review the IRS message on the right.
1. Sign in: https://mytaxes.efile.com/1040/SignIn/
2. If this is not an Amended Return or not checked as such, then the Primary SSN in the Return Header must not be the same as the TIN of a previously accepted electronic Individual return filed for the same tax period. Click on Name & Address and the left and verify the SSN on the right side and or the Combat Zone Code, and Primary Death Date and Primary Tax Payer Signature PIN.
If all SSNs are correct, then you need to print and mail your return. Please go to your My Account and download, print, sign and mail in your returns. Otherwise make correction and re-eFile at no charge.
Here are the mailing addresses: https://www.efile.com/irs-mailing-addresses/
If you have questions, please contact us as soon as possible so we can assist you with your Tax Return.