Triple rates on B 0r G switches on DX6

I have been trying to set up triple rates for aileron , elevator & rudder on my new DX 6 TX using either switch B or G , All is well except for the aileron which refuses to take the setting on 'o' which always goes to 'inh',

Can anyone suggest what I am doing wrong ? All other settings have been relatively painless, so this is rather frustrating.
Many thanks ,in anticipation,

robthos.


.