@Paul & Kurt Thank you for trying to reproduce the error.
Paul i have deleted /Library/Preferences/SystemConfiguration/preferences.plist wich was 5.6mb in size
...
I have found hundreds of "Teensy" modems, I own many Teensys but not that many.
Error is still the same.
There is no other Programm trying to read the data.
Sierra does not trying to connect to the "USB Modem".
@ Kurt
the Error is: Error while setting serial port parameters: 250,000 N 8 1
I have tried:
Teensy plugged directly to IMAC`s USB 3.
Teensy plugged to USB 3 HUB unpowered.
Teensy plugged to USB 2 HUB unpowered.
Teensy plugged to USB 2 Isolator unpowered.
Nothing else running. I have restarted the machine many Times.
Restart with unplugged Teensy, with plugged Teensy, changing USB port, changing USB Cable
@ohhorob Yes I have tried different USB Cables. from 15cm --> 100cm
I also have tried different Teensy Boards.
Edit:
Changing the system language does not fix the error.