Comment 3 for bug 1309445

It also happens to me after fresh install of Xubuntu 14.04.
Network Manager icon has disappeared from Notification area, in plugin properties, I can see that there is Network Management application, which can't find its icon. (It is a grey screen icon, not found icon)
However, "variable applications" such as Guake, Aqualung show thei icons.
Emergency workaround is to install the xfce4-indicator-plugin aside. The combination of the two plugins gives all required information.