I cannot program the Due via the programming port (does not work with the Arduino IDE either)
I get the message
Erzwinge Reset durch öffnen/schließen mit 1200 bps auf dem Port COM5
C:\Users\User\AppData\Local\Arduino15\packages\arduino\tools\bossac\1.6.1-arduino/bossac.exe -i -d --port=COM5 -U false -e -w -v -b D:\B4R\Objects\bin/src.ino.bin -R
Send auto-baud
No device found on COM5
Thank you for the answer.
After applying the solution given below also B4R compiles and flashes the chip:
Several days trying to solve the programming port problem I had also updated the 16u2 bootloader hexfile.
Looking today for the fuses, the clock was devided by 8 which was the problem.....
After changing the low byte to FF, the problem was gone.
In several posts on the subject wrong fuses settings are communicated.