[SOLVED] uploads fail from debian to due: "no device found on ttyacm0"

Using Arduino IDE 1.x
10

I have the same problem as described at the top:
When trying to upload a sketch via the USB Programming Port the following error message appears:

No device found on /dev/tty.usbmodem1421

However, when I connect the Arduino via the Native USB Port the sketch is uploaded and runs just fine.

I am using an Arduino Due, Arduino IDE 1.5.4 and Mac OS 10.9 (Mavericks).
Would the problem in my case also be the Baud rate? If yes, how do I change it on a Mac?

I would be very happy about any help.