i have the same problem. i bought an insurance write-off with a perfect engine, to replace my blown one. little did i know after fitting it that the '97 engine (X12SZ) wants an immobiliser yet the '95 car hasn't got one as the engine (C12NZ) didn't need one.
...so my car is STILL dead!
i will be stripping the donor car down to the shell and literally "get to the bottom" of this issue.
Obviously i wont be publishing my findings as it is a security issue so you'll have to contact me direct.
bookermotors@aol.com
July 2007