I was using 2020 TT Premiere download. I received a number of different messages about why each time I was rejected or not allowed to file. As you have seen from others, the stated TT reject notice reason and the actual underlying reason are not necessarily related. To understand the real reason, we would have to be in a test environment where filing attempts would not be final if in fact it went through. At this point I believe that TT internally lacks understanding of what the bug is and throws out various (sorry about the "various" pun) reasons as to why a return is being rejected. The only thing that seems to be reliably accurate is that involves Foreign Tax Credits.
Conclusion: Ignore the stated reason and review in painful detail every entry, line and box that you have input or requires your input in Forms 1099-DIV, Form 1116 Worksheet and Form 1116 itself. For those of us using the Simplified AMT (nearly all of us) you do not need to touch that form (6251) except to confirm you are electing the Simplified method.
At one point I thought I had things so bollocks that I deleted my Form 1099-DIVs and Form 1116 then reloaded them. Not sure if that is such a great idea, but I was getting desperate to find the solution which turned out to be that long note I prepared that is now shown on Page 1 of this thread as a/the "Solution".
