Shoutbox

Plus toasts are unrelated to the ones of Messenger. Do the following and the Plus ones will go away.

Main MSN Messenger Window > Plus! (the tab at the top) > Preferences > Notifications > Popup Options > Then make sure that Display notifcations when status is set to busy, is not selected. Like below;

Then click OK, or Apply and the toasts for Plus will not apear when your status is set to busy (which will automatically be set when you go into a full screen aplication or game as said by your previous post).

Hope this helps

Edit: Wrong Image, fixed now. Press F5, if the image