eezzeee, create a shortcut to the NASUpdater.exe, right click on the shortcut, and the target field will look something like this:
"C:\Documents and Settings\User\Desktop\firmware folder\NASUpdater.exe"
Add a /force switch after the last doublequote:
"C:\Documents and Settings\User\Desktop\firmware folder\NASUpdater.exe" /force
Then save the shortcut. Make sure TSClient or NASNavigator is not running, then run the shortcut.