If the codes coming out say the near side wheel sensor is the problem - then it will be related to that. It will either be the senor you installed was faulty, not installed correctly, the reluctor ring (on the end of the driveshaf?) is broken (or missing) or the wiring to the sensor is at fault.
I believe if you have the wheel off you may be able to see or feel the reluctor ring down the hole the sensor fits into. Turning the hub you can check all round it.
I believe you should also be able to swap the sensors left to right and see if the code changes.
Interestingly, when I had my codes read recently it was the modulator that had gone - again! I had this done at the main Landie spares place in Chch and they said that they have never seen a Freelander sensor fail - they've had the sensors sitting on the shelf gathering dust for years!