With Ubuntu 12.04 I could not connect to my vanilla Android 4.1.1 tablet as a USB storage device, to copy files between my computer and the tablet. I followed the advice here without success. Running lsusb in the computer's terminal showed that the tablet was connected as a device (and the USB cable was probably OK), but gMPT reported 'unable to open raw device'.
Maybe what I wanted to do is not what you want to do, or your Adroid device may be different than mine, but here is how I got Ubuntu 12.04 to treat my tablet as a USB drive, copying files (both ways), deleting files, and managing directories, etc. in the tablet.
Step 1. remove mtp-tools mtpfs gmtp from Ubuntu (something like
sudo apt-get remove mtp-tools mtpfs gmtp); when this was installed Step 2 did not make any difference.
Step 2. in the Android tablet (not Ubuntu) go to Settings then to Developer Options and turn ON 'USB debugging' so a check mark is shown next to this option - at least on my tablet.
Then I plugged the USB cable from the tablet into my computer. The tablet's memories, internal and installed micro flash drive, were accessible on the computer's desktop.