Well.. this is MP!L not Stuffplug, but we can help you anyhow.
That feature has been removed because it wasn't reliable anymore. Now, it opens whenever a session is started, which is different than a conversation being started. There are scripts for MP!L that have this feature, but as I said, it'll notify you of sessions, not conversations.
A session is when the computer of the other user retrieves information from your wlm, like your display picture, or when you get online.
I'll post a link in a sec
(uhh.. felu beat me to it
)