Arduino Zero's native usb can't work during burning bootloader

I am trying on Arduino zero board. My Arduino IDE is 1.6.13. And the package for arduino SAMD board is 1.6.8. I want to buring bootloader thought native usb port. But there is alway a following error.

Arduino:1.6.13 (Windows 7), Board:"Arduino/Genuino Zero (Native USB Port)"

Open On-Chip Debugger 0.9.0-gd4b7679 (2015-06-10-22:24)
Licensed under GNU GPL v2
For bug reports, read
http://openocd.org/doc/doxygen/bugs.html
debug_level: 0
adapter speed: 500 kHz
adapter_nsrst_delay: 100
cortex_m reset_config sysresetreq
Error: unable to find CMSIS-DAP device

what is CMSIS-DAP? How can i deal with it?

I want to buring bootloader thought native usb port.

What do you suppose the Programming usb port is there for?