Comment 15 for bug 524774

I found the same problem when I upgraded from 9.04 to 10.04.

Specifically, I was remapping another key to Control_L, with

xmodmap -e 'keycode 133 = Control_L'
xmodmap -e 'add Control = Control_L'

But the 'add Control = Control_L' line fails, with the same error mentioned above.

NiñoScript's workaround didn't work for me, but it can't be a permanent solution anyway (as it won't survive x upgrades).