Issue Adding Users to Persistent Chat Rooms

I had a question from a customer recently that was having issues adding users to Persistent Chat rooms.  When they tried to add a user, they would get the following error:

Invalid members: <user>

Checking the category that the room is a member of shows that they added the Domain Users group as an allowed member:

Note: You may need to click on the image above in order to read the text.

Unfortunately this doesn't quite do what they were expecting it to do.  Adding a group doesn't mean that the users in that group, all domain users in this case, are available to be added individually as members of a room.  What it actually means is that the group, Domain Users, can be added as a member of the room:

So what if you want to add individual users as members, but don't want to micro manage the category's allowed members?  From the Understanding Persistent Chat Membership TechNet article:

We recommend, as a general rule, that you use Active Directory containers, such as domains and organizational units, for defining a category’s AllowedMembers and Creators.

So instead of adding a group, try adding an OU.  In this example I added the Users OU, which contained the user account I wanted to add individually to the room:

Note: You may need to click on the image above in order to read the text.

Now when you try to add a user individually, as long as they're in that OU, they are able to be added successfully: