As the error says, your user doesn't have permission to read that device. The easiest way to get permission is to add a custom UDEV filter so UDEV will create the device with the right permissions.

See this: http://puredata.info/docs/faq/how-can-i-set-permissions-so-hid-can-read-devices-in-gnu-linux

Off the top of my head, I would try the following UDEV line:

DEV=="ttyACM*', MOD="666"

That should basically mount all ttyACM devices with read permission for everyone. 

On Oct 8, 2014, at 7:09 PM, pd-list-request@lists.iem.at wrote:

From: Alexandros Drymonitis <adrcki@gmail.com>
Subject: [PD] [comport] ** ERROR ** could not open device /dev/ttyACM0: failure(13): Permission denied
Date: October 8, 2014 at 11:10:42 AM EDT
To: "pd-list@lists.iem.at" <pd-list@lists.iem.at>


I have an Odroid which I use either with an SD card or an eMMC module, both with the same OS (Debian Jessie for Odroid). In the SD card I've got Pd-0.45-5 and in the eMMC module I've got Pd-0.46-0 installed.
With the SD card I can open the port /dev/ttyACM0 (I've got a Teensy 3.1 plugged in via USB) but with the eMMC module I get this error:
"[comport] ** ERROR ** could not open device /dev/ttyACM0:
 failure(13): Permission denied"

Any idea why is that? And how can it be solved?
I've checked the /dev/ directory and the port exists in both the SD and the eMMC.

--------
Dan Wilcox
@danomatika