I blundered around with the schedule B attachment problem for a while, but finally guessed the answer and it accepted my efile without resorting to zeroing out the total carryover which might affect future years. You go to the step by step at File, Print/Save, Save PDF, then choose specific forms and from the list at the right, select 1116 Schedule B, choose save PDF, and rather than having it use whatever name you’ve been calling your return, type in the file name Form1116ScheduleB. It will then save that file name as a PDF to whatever default directory you’ve been saving to, which in my case was Documents\turbotax. When I did that, it still didn’t work, so I added a subdirectory \attachment\ to Documents\turbotax, copied the 1116B file into that subdirectory and it still didn’t work. Finally I added a subdirectory \attachment\ to both the root documents and the root C: hard drive, copied the 1116B file to both places, and it finally worked. I don’t know which one was the right one, but it was either documents\attachment\Form1116ScheduleB.pdf or c:\attachment\Form1116ScheduleB.pdf.
Turbotax should be humiliated by both the tardiness and the lack of directions of how to attach it, but it least it is finally there if you stumble around long enough to figure it out on your own.
