Immobiliser problem

[Craigneukbhoy]

Hi folks

Really need some help here. Went to start my 2008 c30 2.0d but the battery so low it wouldn't turn over. Tried jump-start ing it but with no luck. No I get the message about the immobiliser & it won't even try turn over. Charged battery overnight & refitted but still the same problem.
Can someone please help me from pulling out what little hair I have left.
Thanks in advance for any help.

[Classman]

Hiya my car starts no problem...one day i went to shops,came out,warning message...Battery Flat..immoboliser ,absolutely nothing not even a starter turn over...sat there looking through the manual...after about 10 mnutes tried again and all worked fine..i tried the spare key...works...so i now carry my spare key.
took car for a long run...no longer get the flat battery message,and to date all has been fine...if it happens again try using your other key...o think something must happen to the chip in the key now and again?...