I have usually had better luck with system access.
1.  Create the folder.
2. right click the folder and choose "share on dropbox".
3.  Log in to dropbox, and you will find two edit boxes.
The first is for the e-mail of the dropbox user you want to share the folder 
with, and the second is for an optional message.
They will get an e-mail with your invitation, they will have to reply before 
the folder is shared.
I found in the sharing options, that you can decide whether other people can 
invite others or not.


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