Re: "There was an error during startup. Please see the Log for more details."

@blooobagooo  Normally, you should be able to install a pack via disc without getting an error.  Origin will recognize the pack, or it won't, but it won't cause other issues.  On the other hand, Origin does occasionally get an update that affects Sims 3, so it's not totally impossible that something has changed recently.

Did you get this particular error when you installed the pack, or when you later uninstalled it?  If you only saw the error after uninstalling, then it's likely the problem was a leftover registry entry from the pack that didn't get removed during the uninstall process.

Out of curiosity, which pack is it that you own on disc, and do you own any packs that are newer (by the date EA released them) than this one?

I saw the message after installing the EP (which was University Life), so that's why I figured it may be the issue. I have Island Paradise, but it's also a disc that I haven't yet installed. Also, I just tried to play the Sims again after installing Monte Vista a few hours ago, and it begins to load and then I get a message saying, "Unable to start game | Service initialization failed (0x0175d824)"

@blooobagooo  Can you register Island Paradise within Origin?  If so, I'd suggest doing so and downloading the pack rather than installing via disc, just to keep things simple.  I'd also suggest repairing the game in Origin after installing any new pack, then running the patch again and testing.

Do you get the service initialization error after installing Monte Vista but doing nothing else?  If so, move the Sims 3 folder out of Documents\Electronic Arts (again if you have already) and try to play.  This will remove MV without touching the game's program files.

And just checking, but are you installing MV through the Sims 3 Store site AND using an account that's linked to the Origin account that installed Sims 3?  If not, that could also cause problems.

I only have the disc for Island Paradise, or else I would. When I install University Life, I'll try repairing it and then running to game. 

I just removed the Sims 3 folder from Documents and I'm still getting the message.

I'm 99% positive the Origin account and the Sims 3 account are linked, but not sure how to check. 

@blooobagooo  If you're signing into the Sims 3 Store site with the same email address as you use in Origin, then you're using the same account.

However, that's not the issue here if moving the Sims 3 user folder doesn't help, since that also removes Monte Vista from play.  Moving that folder also addresses some of the other potential causes of this particular error, and the next suspect is a problem with your computer's registry.

You said the game was working again after reinstalling and applying the patch, but now it's not.  Did you do anything else between the last time it worked and when you saw the service initialization error aside from installing Monte Vista?  Installing store content doesn't change the registry, but installing a new pack would.

I understand you only have discs for University Life and Island Paradise, but can you really not register the codes that came with either one in Origin?  You'd need a code to install each pack; the question is whether Origin (or the store site, for that matter) would accept the code.  And since you already tried installing UL, check to see whether Origin now lists the pack as owned.  It probably won't, but it's worth looking anyway.

So I just started the game today, and it seems to be working at the moment--I'm just not sure if that will last or not, and if not, I'll post an update. As far as the two EPs, I have the registration code for University Life but I was using one I found online for Island Paradise, as I only had the disc. I'm going to check on whether or not I can register them in Origin. Thanks for all of the help!