@CarissaM I also uploaded a diagnostic file. Token number is 980088. TurboTax Deluxe download version 0559 running on Windows 10.
I also tried deleting the form 1116 and recreating it as described by @HerbFreiburg but still got the same error.
I also tried to eFile Federal without State as suggested by @lushine but still got the same error.
Note that I'm trying to file an amended return for 2021, for both Federal and California State taxes. I previously filed the original return both Federal and State successfully via eFile. The foreign tax credit was included in the original return in the same way, though I have adjusted some amounts in the amendment.
At the end of review I saw a screen suggesting I print and file with instructions including "Step 2: Print and mail your amended returns. Returns (other than CA) must be mailed." but no explanation why. I saved the resulting PDF, but once I got to filing it proceeded to offer to eFile both federal and state. Is there something about my situation which requires paper filing? I wouldn't expect it to be the case for the foreign tax credit, since I already eFiled the original return successfully.
Update 4/5/2022: Still the same error today, with no new software updates. Form 1116 (COPY 1) and its Schedule B are both present in my list of forms, and my printed return. I was able to file my California state amended return successfully, but am still waiting to file my federal amended return. Since it's an amendment, and I'm owed a refund, I have some extra time compared to the normal deadline. I'd really prefer to be able to eFile, though, to get my refund faster.
