Thanks longtom,
I had seen that before, but obviously didn't look at it properly! Tried the instructions but didn't follow through!!
Otherwise put the following in your ~/.gtkrc-2.0 file (create the file if it doesn't exist):
gtk-can-change-accels=1
That was the bit I missed. Thanks for putting it up. Amazing what you see second time around

.
I'm actually using Openbox but it seems the process is the same regardless. Anyway, works fine on my system.
Thanks again,
Taco.22