So today I restarted my laptop and attempted to boot up TS2, as I do every day, only this time I get an error to the effect of "the target file can't be located". Turns out Avira has put the exe into quarantine. I restore it, and now it says "some needed files were corrupted during installation. Please reinstall this application."

Can I do anything to avoid reinstalling? I always run into a lot of loading and graphical problems when installing TS2 so it's not really a simple case of reinstalling for me. Avira has some done annoying things before but this one takes the biscuit.

I can't help with technical part of Avira, bu I had that problem with Avira anti virus myself and ended up removing it and replaced it with AVAST anti-virus (same thing but handle scanning viruses much better IMHO) and thought my game were a goner when I couldnt play it. But copying the exe from the installation place and make a copy on the deskop (rather than restoring the exe in quarantaine) seems to return the game to normal as long as Avira dont remove it. Also, I doubt you need to re-install the entire game.

I think with with anti virus program you can prevent them from removing programs by adding them to the program "safe" section, but I dont know if Avira has it. Malwarebyte Anti-Malware and Spyware do has it which I supplement the free version of Avast.

But no, you dont need to reinstall, thats Im 100% sure of. Just need find a way to prevent removing programs that are safe to use. (Mine was the lazy way because I hated Avira. Some anti-virus are very crucial when scanning.-)..

It is probably not the anti-virus, but the other functions of the program (registry cleaner, etc.) - I used to use Avira myself and it is a very good anti-virus program, but - and that counts for all anti-virus programs - the extra functions tend to delete some of the dll files that the game needs (most definitely if one uses UC). So does all cc and registry cleaners, so don't use them.

(I don't use Avira since Windows 10, because I got the Windows 10 professional anti-virus along with the new OS).

General:
If you use UC, you will need to repair the game in Origin and then do the things like installing camera mod and graphic rules again - all other cc, as well as your game, should be there, though.
If you have discs, I am not sure exactly what you will have to do, I am not sure a complete re-install is needed, but perhaps ask around first.

Update, with some new problems.

We reinstalled just Mansion and Garden and the game loads again now, but loading any lot results in a tonne of object/food/random popup errors. I have no idea what to do at this stage. I backed up the entire "The Sims 2" folder within My Documents, so the info for everything is there, but I'm getting nonstop popups now.

I think you may have to reinstall, sadly - but if your game is backed up, it should be okay; the missing or damaged files have to be restored and I am not sure how else one can do that with discs. Just put your Sims 2 folder back after, I tend to think your game should be fine when the program files are restored.

If you know what is missing you may be able to copy the needed files off the disk without reinstalling. I would also suggest turning your antivirus program off as some can cause corruption to your sims game. I had one that made babies disappear and borked age up causing $hadsubject memories. It also did what yours did but to another game, quarantined the exe.

It seems to be fixed now with some help at Simbology. Windows Defender was causing the popups but after adding all TS2 related files to the exclusion list the popups stopped happening.