Communication fault on the DATA wire with the engine relay unit
Would indicate a wiring issue or a faulty BSM unit (the engine bay fuse box). There is a network communication problem and the engine BSM can't talk to the BSI.
(edit) as I look through the faults, it could be seen as a communication fault caused my a misconfiguration, rather than a bad connection or ECU.
Error on the VAN interface, more network problems. If your BSI is not configured correctly to the other parts of the car, you will get these odd and unexplained network errors.
I am sure its been asked previously, have you configured the BSI to the other components of the car?
If this is not done, expect odd errors, and if you fail to answer the question, I won't be able to help you any further.
All things considered, I would not suggest a faulty ECU air bag ECU, but my first thoughts would be to check the BSI is configured correctly to your current air bag ECU.
I have had to updated BSI firmware on early cars to communicate with later model parts fitted, which is not really surprising. This is one of the main reasons that advice for parts swapping is to find a donor of the same year, to save the need to update and reconfigure the BSI.