The Kano OS image on BerryServer (berryboot.alexgoldcheidt.com) seems to work now. The following steps worked for me.
Download the latest Kano OS image from BerryServer: https://berryboot.alexgoldcheidt.com/search-downloads/?dl_cat=0&dl_search=kano
The image is compressed with gzip. Unzip it and then copy the .img file to a FAT32 formatted USB device.
Insert the USB device into the Raspberry Pi. Then in the Berryboot main screen hold down your mouse button over "Add OS" and select "Install from USB stick", choose the Kano OS image from the USB device and wait for the copy process, reboot the Raspberry Pi by clicking the exit button. That's it, wait for the Berryboot boot and select the new Kano OS image.