I have this exact same problem right now as well. Can't manually add a 1099-B, just hit a blank screen. It works if I start a brand new tax return file, just not with my existing file.
Unfortunately I can't start from scratch since I already filed my taxes, and I'm actually trying to get started on an amendment since I forgot a 1099, and now I can't add one. Called support and nobody has been able to help me.
Probably won't use TurboTax next year.
