I solved it by changing the Win10 security settings, which apparently was blocking the ability to send.
>> Under ‘Windows Settings’: Search for ‘Change Security Settings’ ...
At the bottom, click on “Reset all zones to default level.”
Now back to TurboTax, and send.
>> OR: using Cortina search, then to ‘Settings’ at the top:
Search for ‘Internet Options’ which takes you to Internet Properties popup.
Go to Security tab.
At the bottom, click on “reset all zones to default level.”
Now back to TurboTax, and send.
Did that work for you?