I just logged in (with IE again) on my second account and got in okay so that account isn't affected, if it is indeed certain accounts. I've been playing with my Blinky account since the very beginning, though I'm hardly caught up, and I registered the Baskin account several months back and did nothing with it other than to make him an ice cream cone.
And both those accounts are fine (though again, with Firefox, it wasn't a Shockwave error that was keeping me out, it was the thing simply timing out after trying forever to load). Anyways, I've received emails from people who are new to the game who are getting the error, so it's not "only" older players, in any case.
(Some people email me asking if I've heard any news on why the game doesn't work, and some ask me to FIX the game. Lol. Yesterday I got one from a person who wanted me to make the mall bigger.
People are funny.)