Hello Rafael,
I don't know off-hand why that should be, but since v4.0 is an old version, perhaps it isn't fully compatible with recent Windows/Java updates that you might have installed. Please try:
- Make sure that all available Windows updates are installed on that PC.
- Run the Hauptwerk v4.2.1 installer (the 'update installer' would be sufficient:http://www.downloadhauptwerk.com/ ) to update/repair the installation.
- Reboot the PC.
- See whether you can then un-install it.