Do people have to login before they are added?
I just checked and the test group i mentiond to have no users now has 3 users in it...

Well that could not be or they would be added before they PM me to complain...

One thing to note on this. They will only be added to that group when they make a new post. What I mean by that, is this:

Say, you set it so they need 100 posts to be in that group. At that time I have 125 posts. I won't be a member of that group until I make a new post somewhere.

So it checks to see when they post if they need to be added to a group, it doesn't automatically add users to that group when you change the number in the control panel.

I am not really sure what triggers when they are added to the group. But I would think that since you just made the group and you have members that already have exceeded the limit prior. That they might need to post one more post to trigger the change.

I just tested this problem on my test board and that what the problem is even though they currently have exceeded the post requirement they have to post once more to trigger the change.

Other that that you could try the content rebuilder to push it along.

Oh well Rick beat me to it I was testing this before I submitted.

I see.
So if it want it to be 100 and have no problems with people under 100 posts I would have to set it to 99 but would still have the issue with those over 100 that only post in that forum?

The people that only posted there would have a hard time guessing they have to post somewhere else first... this is a very bad idea as they will feel resctricted even if they are not... they may even leave the community feeling unwelcome and never figure out they are the one we wanted posting...

Pretty much so.
It looks like the post count uses a >= to not > than value.
If you had this in place since the beginning it would not be an issue today.

Like I said above you could try the content rebuilder but I am not sure if that would trigger the change for everyone. And if your site is very large it could take quite a while to finish.
Scratch this I just tried it it did not work.
Here is the best option to change everyone now.
Control Panel » Member Management
[+] Advanced Search Options
Member Post Count:set your option
Submit
When the list is built you can use the option at the bottom
Action: Change Groups
All Members or Selected Members?
"Perform Selected Action"
Then check the group under Add to.

Thank you for checking on this

What happens if I do what you suggest and next week i want to change the settings to 250 posts? it is obvious that the post count permission settings is going to be changing as needed... as it is not easy to figure out whick post count works best...

I have a feeling that moving people from group to group manually sort of messes up being able to do it in an automatic way...

If you change it from 100 to 250 then think about it.
If you already moved everyone to the group with over 100 posts and you change it to 250. Then all the existing people under 250 but with at least 100 posts will remain in the group. The software will not delete people under 250 they are already in the group.
So you would use the same method that you added members, to delete them. You would just change the search to less than 250. But I would think that would confuse members that once upon a time they could post now they can't.
Of course the members that are currently under the limits that never were in the group will migrate on a natural order.

Just another comment. If you start with 100 and make the changes then change the post to 250 I would leave the members alone under 250 and not try to take them out of the group.
If you reduce the number to 75 you just start another headache that you missed some members that need to be manually added to the group. Unless you wait for them to make another post in another forum. So the script does its own thing.
So I would start with the lowest number. Move the members and just raise it a little at a time.
Just my 2 cents