Thank you.
I did spend some time tracking down the issue and found that if I have never set foot inside the TTD I can save all I want. I can even save all I want after visiting the TTD. The trouble seems to happen after I reload a save after having visited the TTD. At that point if I ever set foot in the TTD again I get the SaveError problem again. I tested this by running through every quest in the building, saving every step of the way with no issue. It was only after I reloaded a save that the problem reappeared. To make sure it wasn't something I did in there necessarily I went back to my save after first entering the building and it too caused the issue where SaveError was happening. Going back to the save just before ever going into the building allows me to go through all of it again without the SaveError returning. However, again, the save error returns as soon as I load any save after having visited the TTD.
I don't know if this is useful but thought I would share.
Also, I figured this might be useful to the others experiencing the issue. You can get everything done there as long as you do it all in one go and never reload a save before you're done with the TTD. That is until the fix comes, and sounds like it will be soon. Hopefully the fix doesn't require going to an earlier save. I suppose in the off-chance it might, take this workaround with a grain of salt I guess.