I haven't done many group outings really, so I don't know what the limitations are.
Does this only occur when you start a group outing and try and have people join? In other words, while you are doing the group outing, I believe there is an option to ask other sims walkin about to join the group. But I don't know if this gets disabled once you group meets a size of 4.
Or... does this occur when you start the group out by making a phone call? When making groups, does it restrict you to only 4 people in the group?
The reason I ask this is because, the few times where I had a Contact call me, and I accepted the invite to go Downtown, when I got there, I was shocked to see like 6 sims pile out of the Taxi plus my own. The group was
definately more than 4. I think it might have even been as many as 7 or 8 sims total, including my own playable sim. It was kind of cool, but also a bit frustrating because I could barely manage to keep them all together. They all kept wandering off, and with no real meter of how tell whether they were happy, I could not make the outing successful.
Ste