Hello triapavl,
If you completely uninstalled Hauptwerk, selecting the option in the uninstaller to remove all settings and files, and then reinstalled the latest version that you do have (presumably v4.0, based on the error message) 'from clean' then it should eliminate that error. However, many v4 sample sets required v4.2 (and so wouldn't work with v4.0), and v4.2 had a lot of improvements and bug fixes above v4.0, so I really don't think you'd want to use v4.0.
The final v4 version was v4.2.1, which would be the ideal v4 version to install if sticking to v4, and if you have a copy of the installer for that saved anyway. However, v4 isn't available in any form from MDA (or anywhere else officially), I'm afraid.
v7 does have a lot of major improvements above v4, and you would be eligible to upgrade your v4 licence to v7, in case you do decide to go down that route.