The Form 1040 is your federal tax return.
If you have not entered any taxable income, do not have a tax refund or taxes owed on the tax return then it cannot be e-filed.
If the Social Security benefits are the Only income to be reported on the tax return, then there is no reason or need to file a tax return.
If you prepared a tax return you prepared a Form 1040.
A 1040 is the tax return form you prepare here to send to the IRS. If you start entering data in this software you are preparing a Form 1040. Please look at it so you will know what you are sending to the IRS:
PREVIEW 1040
https://ttlc.intuit.com/questions/1901539-how-do-i-preview-my-turbotax-online-return-before-filing
Click on Tax Tools on the left side of the screen. Click on Tools. Click on View Tax Summary. Click on Preview my 1040 on the left side of the screen.
What income did you enter? It sounds like you did not enter any taxable income. If, for instance, your only income was Social Security, you are trying to send in a "zero" income tax return. You do not need to file the return -- or if you just really want to file it anyway, enter a bogus $1 of interest as income and it will let you e-file.
Who has to file?
http://www.irs.gov/uac/Do-I-Need-to-File-a-Tax-Return%3F