I've stumbled on this thread by searching google:

It did not have an answer, but one of the posts suggested searching for Shell_NotifyIcon because a similar question was asked that week (which was back in 2010).
So I tried searching for "Shell_NotifyIcon" in that forum, and all it found were topics from 2005 and earlier. How could that happen, given that there is at least one topic with "Shell_NotifyIcon" in its very title, created in 2010?