Luchtzak suggested in the latest news to change the theme.
I reverted to the default webforums_phpbb theme, because with all the other themes that I tried the second title bar (the one that appears under the Luchtzak logo) is not visible anymore.
And since it contains useful features, like Logout Home Downloads Submit News Forums Web Links Top 25 Site Map and the date ...
Well, I have been working on the other themes and corrected the faults. But e.g. if someone still got his 15-inch pc he can choose between a 15-inch friendly theme...
And indeed this theme is the best to use, that's why it is used for guests as well