Can't log into the Sims 3 Game Launcher

After all this time, this answer helped and works. Thank you so much, I was starting to get super frustrated! 

Solution for some:

I've read every help solution I could find on the log in problem when downloading my Sims 3 Store content. I have tons of store content, and was able to download half of it, then suddenly the Sims 3 launcher login screen popped up. I pasted in all correct credentials, and didn't receive any "incorrect" error, but the login screen would just keep flashing up each time.

Deleted all temp files from browser, temporarily removed some user folders, restarted my PC, nothing.

What finally worked: I used my "CCleaner Free" program and ran it. The log in screen stopped popping up, and I could resume my Sims 3 Store downloads. CCleaner removes all cr*p files you've accumulated, and has had a good reputation for years.

I'm leery of 3rd party program solutions, and you may be also: But if nothing else works for you, you may want to give it a try. I've used the program for years--their free version works great. Google the name for the free download.

May want to try it if you're like me, and nothing else is helping.

ElmaFatts, I just want you to know you really, really, really have helped me out. This thank-you is almost three years later, but I wanted to thank you for taking the time to write down what happened and what fixed it. This simple little post of yours has saved my bacon TWICE now. I wasn't able to log into my Launcher, and any time I tried to load a saved game I got a "serious error" message.

Before seeing your suggestion, I fully reinstalled my game and was still getting the same error you were. I almost broke down and cried like a child because reinstalling is SUCH a bear, and it hadn't helped! Then I saw your post and thought "It can't be that easy... can it?" And I did this, and it worked. So if you're wondering if you make a difference in the world, well, to me you sure do. Thank you. The Sims 3 community is incredibly kind and generous, and I think that's a big part of why I keep coming back to this game years after TS4's been out and active in the world! Happy 2019!

were is the IE tools. I'm not very computer smart. Game worked great yesterday. I even uninstalled them and reinstalled them today

@hdni  You can find Internet Explorer by typing it into the search box in the lower left corner of your screen.  From there, here are some pictures to guide you:

https://kb.wisc.edu/page.php?id=15141

The CCcleaner works!! THANK YOU SO MUCH!!! I tried everything but this was the only thing that worked. OMGG SO HAPPY THANKS!!! HERO

Closing this thread as it's a bit of an oldie. If the steps in this thread aren't helping please pop over here "Invalid login/The Sims 3 Launcher Issues".