Immobiliser problem.

I appologise in advance if I may be repeating a problem posted previously by some other members, but I'm at a loss. My volvo is a 2002 S40 1.9D (115bhp version,) 1 month ago it was in my local volvo dealership coz the immobiliser light on my dash kept flashing & I couldn't start the car. Volvo claimed to trace the problem to a faulty glowplug, so recommended a new glowplug set along with a wiring harness and relay. However 1 month later and the problem has reared it's ugly head again, but this time my volvo dealer cant find any error codes using their diagnostic tool. Claiming their previous work cured the problem, & they've washed their hands of the affair since my year's warranty ran out 2 weeks ago. Not happy with them. I feel an argument coming. Never mind, I've tried a few things suggested by previous postees from the search database, new car battery, disconnect battery (all night) but still the same. Help please.:hissyfit:

Non-start. 

Sounds like the calssic 'under the rad' wiring fault to me.!!!! Paul.