How to roll back the latest patch?

I am also running 1.66 and BM 1.12 but haven't encountered this problem though.

I have a game that is on 2421.8 and no hiccups as of yet.

I just started a game with 1.66 and BM 1.12 so I haven't had that problem yet, but I have had the same problem in the past and was only able to get by it by loading an old save game, which would mean hours of lost time, but that always got by the game freeze. I had the problem frequently with 1.63 about half way through a 25 year game. Unfortunately the problem I found with 1.63 is that the game was killing my drive space. By about year 2418 everytime I would play for a couple turns and exit the game without any freezes or crashes I would be missing 300 or so megs more on my free drive space. I had to stop that game, copy all my files off of that partition, reformat it and then copy everything back. I then had the 2 extra gig that I knew I was missing because of SEV. I hope 1.66 doesn't have the same problem, because that would make the game unplayable. I don't remember having that same problem with drive space before 1.63.

I've had just one of these pre-bar freezes: after Cardassian when Cue Cappa was starting. But I saved it (as usual) right before I clicked the turn button, and when I reprocessed the same turn, it didn't freeze.

So how do we go back to the previous version? It seems that 1.66 has introduced more bugs than it fixed.

You back up your save games (and possibly your game type files), uninstall SE5 and reinstall it. Finally you patch it to the version you want, and restore your save games (and possibly game types). If your preferred version is 1.63, you are unlikely to run into compatibility issues.

But let me say that I haven't encountered a single problem with 1.66 yet, and there is at least one post in this thread saying that you may run into the same problems when you are using 1.63.