Fixing MTP mounting error in Ubuntu

I used to be able to mount my Galaxy S4 over USB but for some weird reason I started getting an error message a few days ago. Today I finally managed to fix the problem. First run lsusb to get the bus and device ID:

$ lsusb | grep -i samsung
Bus 002 Device 104: ID 04e8:6860 Samsung Electronics Co., Ltd GT-I9100 Phone [Galaxy S II], GT-I9300 Phone [Galaxy S III], GT-P7500 [Galaxy Tab 10.1]

Now we know that the device is on bus 002 and its device ID is 104. Let's take a look at it:

$ ls -l /dev/bus/usb/002/104
crw-rw---- 1 mostafa audio 189, 231 Nov  7 17:23 /dev/bus/usb/002/104

For some reason, the device belongs to the audio group and I'm not part of that group. So I simply run:

$ sudo addgroup mostafa audio

Then I logout and login and the problem is fixed. As a temporary workaround, if you don't want to logout right now, you can run:

$ sudo chmod 666 /dev/bus/usb/002/104