After more testing I finaly got knx-hdinstall to work. The problem was

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that dialog crashes on my system (and outputs the message Can't make subwindow[...]) when getting german special chars (such as 'ä' 'ö' 'ü' or 'ß') within the --backtitle or --text option.

I would consider replacing those chars with the correct substitutes, a simple

sed -e 's/ä/ae/mg' -e 's/ö/oe/mg' -e 's/ü/ue/mg' -e 's/Ä/Ae/mg' -e 's/Ö/Oe/mg' -e 's/Ü/Ue/mg' -e 's/ß/ss/mg' knx-hdinstall

will do the trick for all of you who have the same problem.

Perhaps someone with knoppix-devel-rights should fix this in the next release for people like us

Allthough I do not understand why only I get this error on my machine, something with localization perhaps wrong on my system?