inSync uses .vbs script files to start and stop the tray application. In insolated cases you may find that running .vbs files has been disabled on a users computer. To fix this, download the registry files from here: http://www.winhelponline.com/blog/wp-content/uploads/vbsfix.zip, and run the appropriate registry fix file (XP for Windows XP, Vista for Windows Vista or 7).
If the registry files don't run automatically, open the registry editor (start - run - regedit), and import the appropriate file (file - import)).