Comment 42 for bug 418470

Mark, I had the same error messages, they are generated because there are two id's that match joystick's name. I don't know which one of the two is actually for controlling the joystick events, so I set properties for both. The errors are for second id.

If you are bothered with the messages, you could change xinput set lines to:
    xinput set-prop $id "Generate Mouse Events" 0 2>/dev/null
    xinput set-prop $id "Generate Key Events" 0 2>/dev/null
(it maybe needs to be 1>/dev/null, I'm not sure)

And, to be free of mouse acrobatics, go to keyboard preferences/shortcuts/custom shortcuts and create keyboard shortcut for activating your script (for example, ctrl+alt+j should be free for use). This way, you'll never see any output, not even the error messages...