Problem: The IRS - not eFile.com - rejected your tax return because you're required to submit a First Time Homebuyer Installment Payment with your return.
Solution: Sign into your eFile.com account, click on My Return, and follow the instructions to correct it. Re-efile your federal and state returns for free. You can also manually search for and add the form under Federal Taxes >Review by searching for "first time homebuyer" and adding the applicable form(s).
Contact us here for further help: https://www.efile.com/tax-service/contact/efile-contact/