By no means an expert on these things but recently had a very similar issue. I called Bobby at GEMM who kindly got the code for my vehicle (which I then input using the key in the lock, etc.). That got mine started but it continued to immobilise following this which was down to water damage in my receiver unit within the car. A lot of hassle/£s later I got a new remote receiver fitted - sorted.
I'd recommend trying to get the right code, input it to see if it starts. Then see if it's going to continue to immobilise following that.
Not sure if this helps but hope it does. Alan.