I tried all of everything mentioned in your comment, and TT still would not install. I called TT support and after many hours on the phone it still would not install.
As a last desperate attempt I started the install and walked away from the computer. I had no expectations that it would install. Imagine my surprise when I returned three hours later to discover TT had been installed. The subsequent update took over an hour but it did finally complete.
So my advice is give it time. I can’t explain why it took so long but it finally completed.
