I'm guessing it doesn't like the VGA text mode.

So, try stuff like
knoppix vga=1
or 2 or 3 or 4 etc.

Also, does it support standard modes, such as 1024x768 800x600

then you could do a
knoppix screen=800x600 noddc
(noddc turns off monitor detection)

I remember seeing a lookup table for VGA modes which would force the linux kernel to use certain resolutions color depths by using vga=xxx where xxx is a number like 792

found it
http://portal.suse.com/sdb/en/2002/1...bdev_grub.html