Engine Performance problem
2001 Rover 75 6 cyl Front Wheel Drive Automatic 91000 miles

my rover 75 cranks over but will not fire up. The previous owner had a diagnostics check done that showed camshaft sensor- no signal and vis balance valve always closed.
I changed the sensor, no different.
I had my own diagnostics check done and it again showed cam and crank sensor no signal( dtc p0340 and p0335), plus it showed ' security code not received (p1666) and immobilisation ecu fault code 0x0f/ random code tolerance increased and bad key identification.
both cam and crank sensors have been replaced with new, so is it the immobiliser ecu, engine ecu, or just a dodgy key? If so how can i rectify?? Help!!!!!