I know this isn't a major problem, but it does bother me.

After I've occasionally downloaded some files for the game, be it any defaults, or even objects, the game refuses to boot up properly until I've deleted the Accessory.cache, and the Groups.cache files. Why? Am I doing something wrong to my game? I am afraid it'll stop working. I do regular back ups, but it would upset me greatly.

No , you aren't doing anything wrong at all. They (cache files) just frequently get wonky. They regenerate on their own , so no harm done in deleting them. I delete mine every time prior to starting the game up. I've been doing that for a few years and have had less random freezing/crashing during that time frame than I had previously. 10 seconds well spent in my book. good luck!

Think of a cache file as a post-it note. The machine uses it to jot down frequently-referenced information so it doesn't take as long to do things. So - imagine it as the scratch paper on which you jot down the phone numbers of all the people you're supposed to call, plus a note of what it's about; then you make the calls and make notes next to each number about what you found out, or what you need to get for them. Any phone numbers you're done with get erased and overwritten.

As you can see, it doesn't take long, on a busy day, for the post-it to become hard to read. Deleting a cache file is just like discarding yesterday's post-it and getting a fresh one. Not a big deal at all.

Thank you guys!! This is very helpful! It makes me feel so much better!

You can safely fix the groups.cache problem by creating a blank window txt file and save it as groups.cache. Save the file you just made to a differant location from your sims 2 folder. Delete the groups.cache file in your sims 2 folder, then move the groups.cache (TXT) file, you just made, to your sims 2 folder. Your game will run fine! I don't think your accessory file is a problem and you shouldn't have to delete it.

Why? The game regenerates the caches just fine as needed.

Perhaps doing that prevents the game from writing to the groups.cache, which would slow things down a little but probably not noticeably, and prevent it from becoming corrupted again?

Oh, I see. In that case would you have to change the file attributes as well?