Did you remember to remove your mods first? And check for conflicts and outdated ones?
Oopsies... Well, I did this today:
I'd completely uninstall, making sure all the folders are actually deleted, and then reinstall it. Seems like a logical first step.
And I deleted everything... mods, saved games, registry keys, everything! 4th speed is still the same, if not slower, than 3rd speed. Ruh roh! I haven't used a significant amount of memory, and I'm pretty sure I don't have a virus. The only things I did before I restarted were update Awesomemod and patch. I haven't updated Windows in awhile, but I don't think that would affect my simming.
Also, I found out that if I crack the game before I patch, I don't get that error message.