Why do I have to enter at least one for the number of days in the US on Business under the physical presence test?

What form are you filing and why?

Are you a US Citizen or Resident?  If not, then you would need to file a 1040NR which TurboTax does not support.  You can use Sprintax.com to file the 1040NR.

I am a permanent resident but I was overseas during the tax year.

Then place a "1" here. This will not have an adverse effect in your tax return and will allow you to move on in your return.

I currently live abroad (and have for years) and am filing my taxes. I am a US citizen who visited the states during the summer last year to visit family. I am also having this error where I am being asked to enter "1" but I have not done business in the US since I have moved abroad. How can I fix this error? I don't feel comfortable declaring that I have done business in the US during my time living abroad when this is simply not true

You may try entering 1 just to move past the error. It won't impact your return.