Hi edgardnetz,
It has been reported that OpenSDA v2/2.1 bootloader could be corrupted when the board is plugged into a Windows 10 machine.(You can find the information at OpenSDA)

If you are using Win10, you may need to use external Programmer Flashing the Bootloader into K20.
And then Reprogram your OpenSDA adapter with Lastest DAPLink rev0244 firmware application.
Best Regards,
Robin
-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------