Can't upload any sketch to Arduino MKR1000

Hello,

Today I got a MKR1000.

I use Arduino IDE 1.8.5 under Linux (64 bit). I use it successfully with some Teensy boards.
I

  1. installed the board driver(s)/tools for the MKR1000 via the Board Manager and restarted the IDE,
  2. selected the "Arduino/Genuino MKR1000" from the board list,
  3. connected the PC via USB with MKR1000 (the preinstalled sketch "blinky" starts and runs).
  4. selected the default serial device ('/dev/ttyUSB0'),
  5. and connected my USB-UART adapter with selectable voltage (set to 3.3V), pin Rx of the adapter
    to pin 9 (Tx, digital 14) on the MKR1000 and pin Tx of the adapter to Pin 8 (Rx, digital 13) on the MKR1000.
    Calling the "Get Board info" displays
BN: unknown board
VID: 067B
PID: 2303
SN: Upload any sketch to obtain it

As I understand it, something is going wrong... :frowning:
When I try to upload any sketch by pressing the button "Upload", I get the message

An error occured while uploading the sketch
No device found on ttyUSB0

I've reversed the wires on Rx and Tx pins, but the result didn't change!

What do I wrong?

Thanks in advance,
Michael