I had to install Gnomad2 in Ubuntu Dapper in order to upload files to my MTP Mp3 player.
I followed this great How To
However Gnomad2 could not open the device unless I was root (same thing for mtp-detect)
It looked like a permission problem in /dev/bus/usb
This worked for me :
In /etc/udev/rules.d/40-permissions.rules
I changed
# USB devices (usbfs replacement) SUBSYSTEM=="usb_device", MODE="0664"
to
# USB devices (usbfs replacement) SUBSYSTEM=="usb_device", MODE="0664", GROUP="plugdev"
Then
sudo /etc/init.d/udev restart