The pot is linear yes. When only one HPWM channel is used, the system works fine ie. as the pot is adjusted the motor speed increases as expected, likewise, if the motor is disconnected the solenoid works fine. But as soon as both are required to function together that is when it messes up.

It seems as though the Duty variable that is being sent to the motor is also being sent to the solenoid, but the solenoid has a completely seperate duty value of its own.

I shall try and post a schematic.

Hugh