Range Rover Immobiliser Problem!!!!

[RCA]

Hi all, wondering if anyone can shed any light, I have a 97 4.6 HSE which has kindly decided to deem the code in my key useless so I have to open it with the key not remote, This will not disarm the immobiliser thus needing to enter the security code with the key, I have tried this and can not get it to work!!!!, Has any one else had this and know any tips!!!!
many thanks
Richard

P.S. If it is sensitive info please e-mail me
cheers