Windows 7 changes the default functionality of the System Tray to hide icons created there by default. Instead, users have to click a strange up arrow:
It can be fixed per user and per application by clicking Customise, and changing icons to “Show icon and notification”.
There is also a checkbox for “Always show all icons and notifications on the taskbar” – again, this is per user.
To stop this behaviour for all users you can force all System Tray icons to be visible on the Taskbar in regedit. Open Regedit and find:
Create a new DWORD value called EnableAutoTray. Leave its value as 0 (zero). Log off and log back on or reboot and regardless of what you have previously set, all icons are now visible. Setting it to 1 will set it back to default for everyone, and removing the key lets you define it per user by putting it in HKCU.