Help needed with immobiliser issue not starting

[dan-T]

Ho, looking for help I have a Forester 2009 diesel and she has developed a problem, she will start on the button run and rev for about 3 seconds then cut out with the immobiliser light illuminated and won't start again until I turn it off and on again.

Then same thing happens, I've had keys recoded and taken it to a specialist auto electrician who believes it's a problem between ecu and immobiliser not communicating properly but said only Subaru can fix this, hired a transporter and drove it to Subaru in Derbyshire and they said they don't know what the problem is and can't do anything with it? I'm now stuck any ideas? Thanks Dan