If its a B engine going in a C its not something stupidly simple like your not running a MAF on the Vec C ECU but the B set up, or your Vec C was a "Direct" and your putting an SE in not a YH? Its not an Estate is it?
Also just reading your first post, I could point you to loads of threads on the C sites where there cars aren't starting when left for a day with no running, I'm having the same problem at the moment, this cold spell is causing havoc with something. I've notices with my car, I presume the Astra and B will be the same that if the battery is just slightly low the Starter just clicks, it doesn't turn slowly like my older cars, the battery has to be in tip top and all earths good. The ABS comes into play as well, if the ABS plug is dirty it messed with the CIM, my plug was dirty, it cause the immobiliser to stay on, dials to stop working and a load of other things, so many thinks go through the CIM. The Vec C immobiliser is Cat 2 so it has to cut both Ignition system and fuel pump so I may be and probably could be wrong but if say the pump isn't connected right then it could throw an immobiliser code dunno.. TBH is way over my head, Carbs and good old fashioned Relays I can handle but modern cars are a pain in the rear. Maybe Benny could throw you a check list of systems to go through.