Burning bootloader on Mac: troubles with mkII

I'm trying to use the mkII (usb on the JTAGICE version):

avrdude: usbdev_open(): did not find any USB device "usb"

I'm using Mac. On Windows I successfully managed to write to the AVR however (with AVR Studio 4).

In addition to that: AVR Studio doesn't accept the optiboot 328 file although it seems optiboot is saying it should work for both the 168 and the 328.

I compiled the code for Atmega168. It uploads to the 168 but Arduino isn't very pleased with it:

avrdude: verification error, first mismatch at byte 0x0002 0x36 != 0x34 avrdude: verification error; content mismatch