I have attached a picture of the error message. Basically, no matter where I try to open the game from (Origin, shortcut, start menu, what have you), the game will display the attached dialog box and terminate. I had this problem for years, and then I noticed that there was no Sims 2 Ultimate Collection file in my EA GAMES folder. Alright, cool. Uninstall, reinstall, works fine...for one session (about two or three days ago). Now this is starting again, only this time, there is definitely a completed Sims 2 Ultimate Collection file where it should be, everything looks fine in the Programsx86 file, and I'm not running with mods, so it's not that. If it comes down to it, I still have my original disks from before the Ultimate Collection and I'll play it unsupported, but I would rather not.
While I don't have any mods installed right now, it is pertinent to note that I edited the screen resolution according to this tutorial (https://simsvip.com/2014/07/20/the-...solution-guide/) and I had that Ego camera thing for my game for about 5 minutes before I didn't personally care for it and reverted the file back to where it was previously (you can find that here on MTS: http://modthesims.info/download.php?t=504385). Did I mess up the game by screwing around with the files? I followed all the steps exactly as they were presented, so I don't see why it would be a problem...
I'm running Windows 10 on a beefy HP Phoenix computer tower with an i7 processor, an nvidia geforce graphics card, with either 32 gigs or 64 gigs of RAM (don't remember which one, but I do know it's a lot because this computer runs like a dream most days), a terrabyte hard drive that's about half-full and another terrabyte for an external hard drive. My screen resolution is 2650x1440...not sure if any of this helps, but I'm just gonna throw it all out there now in case any of it's useful.
Is it because I'm running Windows 10 instead of Windows 8? Am I going to have to uninstall and reinstall the game every time I want to play? Any help or insight would be appreciated for this matter.

Have you tried deleting the cache files? They can sometimes cause troubles with startup, often when you've run the game fine last session but have troubles the next gaming session, when you've run Bodyshop, or when you've added or removed CC.

(Groups + accessory, and Contentregistry + Cigen if you've run Bodyshop)

Editing the screen resolution could potentially be the problem. If the game runs fine with the presets, but doesn't run at all with a custom setting, it's possible you've done something wrong.

Check your antivirus. Make sure the SIms 2 gamedata and userdata files are added to the exclusions list.

If the av software is scanning the files when the game needs to access them, then it will assume they are not there.

Just tried that, same issue. Good thought, though, I forgot about the cache files...

Right click on the UC icon in Origin and do a repair on the game, but first remove any hoods and CC you want to save.

This may have been caused by using a registry or cc cleaner - those tend to delete some of the .dll files the game needs. You will need to repair it, as Marka says.