If the gross rental income is $8700, then there isn't a need to file.  If the $8700 is the net income, maybe.  If the gross rents received is over $13,850 then you need to file.

With mortgage interest on a rental, and a rental means depreciation and other operating costs, why would you not file?

Not being able to e-file isn't the Tax regulation for reporting. There is something going on that means it doesn't qualify to e-file, such as required forms or info, or something about the taxpayer's situation you haven't described.

He also has social security income for himself and his wife for 16,182. The system is giving me an error code stating that all of the following lines on form 1040 have zeros, which is the reason I can not electronically file.

Awesome Thank you! it worked 

You're welcome.

Any idea of why that works?  I'm intrigued by the question of where to draw the line between common sense and ethics.  Would it be OK to add $100 of imaginary income, to satisfy IRS computers?  What if people have to show their returns to state agencies to collect some sort of benefit, and it's turned out because it looks like they are hiding assets?

I think the IRS specs prohibit efiling "zero" returns. I have been known to label that interest income as 

"entry needed to efile"

Sometimes I might put it in as Misc Income.

But it's not a zero return, right?  Do they do that with every return below the filing requirement, or just those with rental?  I would probably do the same thing if I weren't such a fan of paper returns.