Check the earths. Also get your nose in the fusebox for signs of burning, pull the relays and maxi fuses out if needs be. If it's a second hand fuse box, it doesn't mean that it's 100%.
You can also check that all power wires and the earth wire feeding the becm, attached to the stud connectors by the fuses (Earth is the extreme left black wire) are secure..also do a "Sniff test" on it.
Normally, multi fault messages at the same time, especially fuse faults tend to be fusebox related. Multiple ECU related faults can be either a bad supply to the Becm or Becm connection problems. All ECU's communicate via the Becm which in turn flags them up on the message display.