Hi chrys2611, Welcome to the best Sims forum on the Net.
I am replying to your post to offer you friendly support so that you will know that other's may have or had the same situation happen in their game.
Unfortunately I do not have an answer for the problem you are having in your game because the same thing has happened in my game, not in Twinbrook, but in Sunset Valley. Fortunately I have learned to save my game often, opting "save as" instead of just "save", so that I have many back ups to save me from losing too much of my game time in the event that my computer crashes, or the save error codes pop up. Yes, it is very frustrating and believe me, I, and many other forum members feel your pain as well.
I'm not sure that we can recover our game file as it is probably too corrupted. When I tried to save, I got the message "processing" too. It processed forever and I also had to exit the game the same way you did to get out of that screen. My Son is more computer savy than I am and he told me the computer would probably never finish processing because it was trying to search for something that did not exist. This same problem happened to me in "live mode" when I was in active playtime. I was in mapview and clicked on my active household and when it tried to load my house the computer or game glitched and my Sims pictures disappeared and the box at the bottom of the screen was gone. I zoomed in to see inside of my house and my Sims were not there and there was an empty house icon that indicated that nobody lived in that house. I had scrolling ability, but I had no mouse onscreen and there were no options anywhere to click me out of that "mode/screen". I had to exit the game by hitting "alt/esc", or something like that. (sorry, I can't remember exactly which button I clicked to exit, but it was either "alt/esc, or ctrl/esc" I believe.
Hopefully one of our "computer experts" here on the forum can correct or confirm this information about the computer "processing" while trying to save. We have some really smart people here on Carl & Pam's Sims site. Be patient, these are really nice people that are always more than happy to help you if they can. We have a very friendly atmosphere here and have fun sharing game experiences as well as helping each other out when we get in a jam. Good Luck.