Best to send debug to the team,
check here http://community.nightdev.com/t/debugging-the-streamtip-alerter-not-the-visual-alerter/1306
You don't happen to have 2 Streamtips installed? I don't know if this causes this issues but I know one of our recent builds didn't copy over an existing install so sometimes users have 2 Streamtips installed.
I had an issues before where Streamtip didn't seem to connect so I ended up deleting the folder in AppData ( C:\Users\USERNAME\AppData\Local\streamtip-alerter ) and reinstalled and fill everything out.
But sending a debug might help Night and the Dev team pin point the problem asap.