So basically, I have a pool and nobody swims in it (usually people jump right into pools immediately...?), I tried to make my sim swim and then invite someone to join but the action immediately disappears! Why?

I have made the pool into a "death trap" by building a fence around it and only allowing people to go in via the trampoline (so they can get in but not out), and I thought that may be the problem but I tried removing the fence and adding a ladder but I still can't invite someone! What's wrong?

Nobody? I really need help, this kind of messes up my entire gameplay

UPDATE:
I haven't had this problem earlier or since. Still can't get people to enter that particular pool but when I played another household and hosted a party at the local pool everyone went swimming and I could invite people, so it must obviously be a problem with that particular pool I described. As I said, I tried removing the fence and adding a ladder but that didn't help, so what's wrong?

Did you try draining out the pool and refilling it with fresh water? Maybe all the guests are turned off by the smell of all the sims you knocked off in it before deciding to use it for entertainment of a different sort. I mean, really, that water must be pretty skanky after a bunch of sims were trampolined in to drown over all that time.

Whoops, that would be my lacking English skills! I meant diving board. In my native language, the word is "trampolin" so I accidentally wrote that, without realizing that the English word "trampoline" is something entirely different. My fault!