You are right. I forgot the "FRAMEBUFFER=/dev/fb1 startx" command. It's working now.

Thank you all very much.

Hi, I have bought a Adafruit PiTFT - 2.8" Touchscreen Display for Raspberry Pi. There’s a descripition for the installation of the touchscreen Display under https://learn.adafruit.com/adafruit-pitft-28-inch-resistive-touchscreen-display-raspberry-pi/easy-install . I took the easy install possibility...