Immobiliser p1611

My daughters Micra with the keyless ignition has developed a fault. It had been parked up for about 3 months without turning a wheel or being started. Battery was totally flat so I charged battery up and checked it, battery was fine. Key fob opens car on button. The green KEY light flashes up when ignition is switches on but doesn’t start. There is nothing it’s not turning over. I plugged my Delphi in and read the code p1611 which I believe is an immobiliser fault. The Delphi won’t let me reset the immobiliser. Anyone know what to try or where to go?
Have a look at the immobiliser fuse in the interior fuse box, replace it its a 10amp fuse and check if any luck