Immobiliser Issue

[martin1200r]

Folks, don't know if you can help, my sons replaced the starter motor on his VTR but now the immobiliser won't recognise his key and the key light on the dash blinks repeatedly.
I've had a search on the forum & there's lots of immobiliser problems but I can't understand how disconnecting the battery would cause the immobiliser to go belly up, any ideas?

Thanks

[Chipwizards]

It shouldn't do but it's not unknown to have problems.

First thing to do whenever you have a problem is to revisit anything that you have touched since it last time worked properly.

Sounds obvious but you wouldn't believe how many times I've been told "Oh yeah, I took that off to fit 'xxxxx', I didn't think to look at that" after I've spent five hours diagnosing a fault that was introduced, rather being a component fault. People never want to pay for the five hours finding something that they could just have told you in the first place.