The problem turned out to be that someone was trying to hack into my TurboTax program while I was working on filing my taxes. It came to light when an email from Intuit/TurboTax told me I'd been idle too long and I had to log in again, and the login page had an incorrect phone number and would not allow me to change it. When I called the "fraud unit" and we changed the phone number back to my correct number, the transmit page and button then worked fine.
