K4M Laguna 1 won't fire after engine swap?

I hope someone in the knowhow can enlighten me somewhat about the inner thoughts of Renault engine control...

Patient is a 1999 Lag 1 PH2. Donor vehicle is the same year but a few months younger. Swapped engines, but kept Patient's ECU in there so there would be no problems with the immobilizer. Engine would turn over, but not start. No spark, no fuel injection. Just as if the immo were active (but dashboard said all was okay).

On a whim, I plugged in Donor's ECU with donor's immobilizer magnet in the key. Car said immobilizer active, vehicle will not start, immo LED flashing(why???). Lo and behold, turning over the engine fired up!!! Swapped immo magnets back, immobilizer turned off, engine started again!

Plugging Patient's ECU back up, engine will not fire again!

I am guessing Donor's ECU has had the immo knocked out?

This is a confusing mess... so... could anyone tell me the following information:
1. Where is the IMMO code stored? The ECU, or the instrument cluster?
2. Does the ECU only have an IMMO ON/IMMO OFF setting in it?
3. Why wouldn't my original ECU start the engine if the immo was not active?
4. Are injectors coded to the ECU (or vice versa?) in the Sirius 32 system?
5. Is it possible that Patient's ECU won't start the new engine because injectors are not coded to it (or vice versa) ?

My problem is that seeing how with Patient's ECU, the engine will start regardless of immobilizer status, I am guessing someone had the ECU's immo setting knocked out. How do I fix this? I do want the IMMO working...

NOTE: I am -NOT- interested in disabling the immo, so please don't report this thread before reading through it properly.

Thanks for any info in advance guys!

K4M Laguna 1 won't fire after engine swap?