There is already one user store created in the VIP gateway.  When a second user store is added, it will not allow the user store to be saved.

Submit option for the user store is greyed out.  Some other options are missing or greyed out.

The user filter in the first user store can cause this problem if there are quotes - " " - around the container or group.  

Remove any quotes from the user search filter from the first user store, then save and try creating the second user store again.