renault kangoo 1.9 diesel immobiliser fault?

[CarlW]

hi,my renault kangoo immobiliser is playing up, what happens is when you turn the key in the ignition the red light should stop flashing and go permanent red then the car should start, but it doesnt, but if i turn the key backward and forwards a few times in the ignition that does it i.e it the light goes permanent and it starts !! any ideas please,thanks carl
the key is nice and tight in the lock