Although I don't know anything about your particular mobile excrement,
cruise controls systems in general take an input from the brake and clutch
via a microswitch, this is to allow an immediate disable of the CC
function when you push the clutch or brake pedal.

If pulling the pedal up with your foot before you enable CC allows it to
work then you have a dodgy switch or pedal assembly.

The microswitch is probably sticky or in need of adjustment. Perhaps the
brake pedal has too much free play and is allowing the switch to sense a
closure. Try squirting some aerosol ghee into the switch (in case of
sticky switch). If there is too much free pedal travel it is probably
because the pivot hole is worn oval (Mitsushitty are not known to use good
quality metals) - maybe you can rebush the pivot hole.