I’ve gotten reports that certain private servers do not work when joined via link.
For example, when I try to join Big Brother - Roblox it gets stuck on “Requesting server” for me and certain people. Someone even tried waiting 20 minutes to join, but it seems to be permanently stuck on “Requesting server.”
It’s inconsistent, as I can join some private servers of other games.
possibly related:
http://devforum.roblox.com/t/what-causes-an-infinite-requesting-server-screen/25380
This only happens on Private Server links though, I can play the game normally if I press the green join button 
Interesting. I recall this happening to me with Apocalypse Rising - my friends couldn’t join unless I added them individually to the Invitation list. They’d get Requesting Server instead.
More info after a little testing:
1.) Your own Private Servers always work for you.
2.) If the private servers has “Friends Allowed”, and you’re a friend with the owner of the Private Server, you can join it with no problem, even with a link.
3.) If you are manually allowed, you can always get in.
4.) If you join via link, are not manually allowed, and Friends Allowed isn’t checked, you are stuck on “Requesting Server”.
I’ve tried this with 4 games, my own game, Murder Mystery, Roblox High School, and the Big Brother link posted in the description.
Happening for me right now, I think wish_z got how it works down