Originally Posted by
cordelli
It was a warning message probably for an application or task that crashed, leaving the icon in the system tray. It lost the connection to the application that put it there, so when you right or left clicked on it, there was no information for it to display.
An icon associated with a crashed app will simply disappear on a mouseover event. If the OP was able to hover on it and it remained visible then it wasn't a crashed app.