Flashing Immobilizer Light

[Doily]

After changing the timing belt on my 2003 1.1 Saxo the light on the dash constantly flashes with the ignition on.
The car starts and drives normally, with the light constantly flashing.
Has anyone got any ideas please?
Thank you very much in advance.

[wheeler]

Did you have the battery disconnected?
Is it the key symbol that is flashing?
Did the light used to come on for a second or two then go out?
How long have you owned the car? Is it possible that someone has re flashed the ECU to remove the immobiliser?

[Doily]

Thank you for your response. I did disconnect the battery before I worked on changing the belt. I have owned the car for 12 trouble free years (I fitted a new belt after I purchased the car). It is the key symbol that is flashing. It used to come on for a few seconds when turning ignition on. I have tried the spare key with same result.

[wheeler]

Quite a bizarre issue, i would have expected the engine not to start if the key light is flashing.
Only things i can think of trying is disconnect the battery again for a few minutes & re connecting, make sure the key is out of the ignition when you disconnect & reconnect the battery.Failing that i would maybe try just leaving the ignition on (without the engine running) for 10-15 minutes to se if it re sets.
Option 3: take the bulb out

[Doily]

Thank you again for your suggestions. I've just tried the battery disconnecting and ignition on ideas as you suggested. Unfortunately the light still flashes. Best regards.