The portals are the spots on each side of the lot (on the sidewalk and street) where sims and vehicles "appear" when they enter the lot and "disappear" when they leave the lot.
What version of the game are you playing with, is it patched and what hacks do you have in game? Is this only happening on community lots and is it on ALL community lots or only specific ones? If you have NL, did you go to the community lot using the taxi or drive a vehicle? Is this the first time you've been to these community lots or have you been them before and haven't had problems with?
I have the original,NL and U. These are lots I have been to before and I am getting there by car I haven't been noticing it happening on my residential lot the mailman and everyone else seem to come and go just fine. It is happening on all my community lots not just one version of the game or one lot. As fas as it being patched I really can't remember if I patched it or not. I had several different hacks, but removed them all thinking that one of the hacks was causing a conflict. I used the clean pack installer from MTS2 to find them all and get rid of them. Is it possible that not all of hacks were detected and I am missing something. I didn't install any hacks using simpe they all went into my download folder. I can't remember all the hacks I guess I should have written them down (my mistake). I guess I'm not much help huh. Sorry.