Keep trying the erase force, it should work. It might also be a good idea to restart computer or power cycle completely.
I managed to flash it but now i get this error:
"The last USB device you connected to this computer malfunctioned, and Windows does not recognize it."
And the device is named "unknown usb device (device descriptor request failed)" in device manager.
It also doesn't work with other computers. The keyboard worked yesterday, this happened while I was reflashing it to change the keymapping. Is the usb connector on the board broken or is there anything i can do to fix this?
EDIT: the connector on the board is a bit loose, maybe I need to resolder it? Mind you that flashing the board does work... sometimes (I did it many times and sometimes it worked and sometimes I get the memory write error, don't know what I did different the other times. The atmel driver is installed and appears when I connect the board, so I was indeed stuck in DFU mode, but now I got out of it and get this USB malfunctioned error.