Today, April 21, I tried again, "just for kicks" and it worked. I was able to Netfile. I did nothing different. And there was no update when I opened TurboTax today.
While I am relieved that this is finally done, I remain profoundly unimpressed by TurboTax: support was terrible and the lack of information regarding the cause of the problem was just as unacceptable.
Next year will be...well...another year.
