Mods that fix the Game ?

I'm not having any errors in my game at the moment, so I'm not sure about recommendations for that. What problems are you having specifically?

I can give you the mods that I absolutely would not play without, many I've been using for over a decade. Most I got from Mod the Sims, some from More Awesome Than You, some from specific creator's sites. Hopefully you can search Sims 2 along with the mod descriptions or names to find them. There's a lot, I'll have to break it up. 

The Anti- nag about subhoods mod. (I can't put the name here because it will get filtered). I like that one because sometimes I don't want to add Bluewater Village and I don't want the game popping up and telling me I should add it every time I start up.

Auto secret door. Opens the secret bookcase door automatically when your Sims want to use them. While doing the "pull out a book to unlock the door" action is cute a few times, it gets annoying very quickly.

Base Game Career Rewards as Aspiration Rewards, Freetime Career Rewards as Aspiration jim TNW, and University Career Rewards as Aspiration jim TNW. These move the career rewards into the aspiration rewards and gives you the ability to get them with aspiration points instead of only being able to get them when you do certain careers. Want to be able to call the grim reaper without being in the paranormal career? Then this comes in handy.

Boiling Oil's No Trash Memories and Phones for All. The first one stops annoying memories from being saved. Like, when your Sim sees cockroaches. That's funny once, not ten times. The second one checks the "phone" box for all townies so you will be able to call them on the phone once you are friends. Normally you cannot call townies on the phone because they are homeless with no phone.

Bribe the Headmaster Object. The headmaster scenario is fun to try once or twice, but it's nice to just use this object and Bam! Your kids are in private school. Now, this one does have a bit of an error rate with Legacy that it didn't have with UC. Sometimes it pops up and tells you that you do not have enough money or that your Sim is not gold or above, when those things aren't true. The best thing to do is save before you use the object, then when this happens, go back to the main menu without saving, then come back into your lot. Let another Sim day or two pass and try again. 

No baby harassment. Keeps Sims from constantly trying to pick up and play with the baby and then leaving it on the floor.

No bladder loss from seeing transformation. Comes in handy if you have werewolves.

No Dormie Regen. Keeps the game from generating oodles of dormies. I generally take it out, let the game generate some dormies for the dorm I'm in, then put it back. There won't be any new ones generated, even if my Sim moves or a I move out a dormie, as long as it's in the downloads.

No Enemy Visits. It gets really annoying having them constantly show up and knock over your trash can.

No Hobby Spam. Stops the game from spamming you with hobby related stuff.

No Jealousy At All. I put this one in whenever I'm playing a romance Sim. Because having a lover walk onto the lot when your Sim is with another lover can quickly ruin your efforts towards meeting their lifetime goal.

No Random Calls Contacts, No Random Calls Dates, and No Random Calls Subscriptions. Because those are annoying.

No Route Fail. Technically, Sims will still have route failures, but it stops them from throwing a fit when it happens and simply continuing to stand there. They will instead simply pick a new route (they aren't truly stuck).

There's some from Cyjon. Fewer Lighting fires, which is pretty self explanatory. No Neutra Spell Alignment Shift (the l is missing in neutral in the package name), which stops witches from moving toward one side or the other of the spectrum when they do neutral spells. No Return Home Animation, which stops Sims from doing certain actions every single time they or another Sim come home.

No Wolves. Normally the werewolf comes to Sims lots every single night. I have a Sim Transformer, so I don't need them hovering at my doorstep every night.

There Can Be Only One Professor. You have to have this in place before adding a University. It makes the game generate one professor for each subject instead of two. Just cuts down on clutter.

No Stray Respawn and No Townie Regen. Keeps the game from spawning a ton of strays and townies. This is especially nice if you use SimPe and/or cleaned neighborhoods and start with a reasonable number of townies.

No vanish in dorms. Ensures visiting Sims and Greek House members don't go into a dorm room and never come back out. Makes it hard to interact with them when they do that.

Self Exploding bottles. Sims leave baby bottles everywhere. You can either make Sims go around picking them up or install this mod. The bottles will disappear several seconds after they set them on the floor.

Sim Transformer. It's a painting that you can use to make your Sim into an occult Sim. Handy when you don't want to take the time to befriend the necessary Sims, wolves, or get abducted to get an alien. 

Slow Motive Decay Indoors Vampires. Slows vampire motives while they are inside. Gives you time to move your vampire Sims through the house and makes it less likely they will die before reaching their coffin. Especially handy when they randomly decide to get up to get the mail in the middle of the day and you need to save them.

Visitors Will Behave. Makes visitors behave and not mess with things in your house you'd rather they didn't.