I solved my Problem!!! For other users just this info : I' am using normally a PCI Grafics Card Matrox G450 - because of dual display usage. (I use it on any PC i work with). This causes my trouble. I changed the Bios to internal Graphic card (i845) only - and all knoppix worked wonderful.
I think knoppix could not resolve multiple Graphic-Cards or special Konfigurations like mine (PCI-Graphic Card and internal Graphic Card off!!!)
So maybe this Problem is a Problem of graphics...
Roland