I solved the issue once and for always as follows: goal is to create a registry entry which will launch the tray icon for you. Start > Run > regedit. In the regedit user interface drill down as follows: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

You should see folders on the left and some icons and text on the right. In the upper left of the Registry Editor click on Edit > New > String Value. This will create a small dialog box on the right side waiting for your input. Type TrayIcon, hit enter. Now double click on that icon. A dialog box will open. In the dialog box enter the path to avastui.exe, usually on your C:\ drive. In my case the result looks like this and please note the command at the end of the entry: c:\program files\alwil software\avast5\avastui.exe /nogui

Once you enter this string command, click OK. Close the registry editor, restart the computer and you should see the tray icon. Now, it has no choice but to appear until you uninstall avast or get a version of avast that changes the path to the command file. Works for me, hope it does well for you.