hi DivinylsFan
it sounds like your game had an old bug see here
http://sims3.crinrict.com/en/2011/04/bug-crowd-gatherings-on-community-lots.html
now i havent seen too many people report this bug recently so my question to you is what is your game patch?
and let me say i totally agree with Sue_D_Nim the first set of advice your rec'd are solid ways to handle this problem
and if you modded sims 2 you should really stop by nraas and fill up - sims 3 has more games glitches and nraas is the answer to most of them.
also i when i first started playing sims 3 i thought my sims 2 knowledge would make playing the game easy. wrong :) i couldnt even place an empty lot and had to google the answer. just know the UI for sims 3 is different enough and only very few things are the same in terms of cheats and game play
so see if this guide helps
http://www.carls-sims-3-guide.com/
good luck
