I bought a decat with a MIL Lambda Elbow (prevents MIL light coming on by moving lambda sensor further away) which worked perfectly on my mostly standard 220 Exige S for about 4 months.
I recently (2days ago) had the 260 upgrade with the addition of a 2bular manifold and new decat, forgetting to move the MIL elbow the MIL light came on due to O2 readings as you would expect. Dohh.
I then fitted the MIL elbow from my old decat and cleared all of the errors with a scanner and drove home with no MIL, yay.
Just washed the car and when moving car into the garage the MIL came back on!? Arggghhhh! HELP.
Elise parts MIL eliminator on mine never had any bother.
Just switch it back off with a cheap obd tool…
Thats what I had done earlier.
Think for some reason the Lambda sensor needs moving further away from the main pipe?
You sometimes find that after initial installation of the extenders that the sensor will still be tripped a couple of times. After swapping it out (or swapping the cat back in), I’ve tended to find mine needs a couple of resets before it settles down and learns it’s setting.
Thanks mate, I decided just to extend the MIL Elbow another 1" and after resetting about 300 miles ago I have had no issues since 
Black tape seems to work also 
My light just came on this morning, that’s with 2bular manifold and decat and after my 260 upgrade. where did you get mil elbow/extender from
I have one Phil I don’t use anymore, drop me a pm and I’ll send it out tomorrow.
Just in case that falls through, this is the extender I added on to my existing MIL Elbow: http://www.ebay.co.uk/itm/251317571511?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
I use the same one with no issues
Great look forward to receiving it not sure why it only came on after 260 upgrade as I’ve had decat on old manifold for months and all was fine. Unless a lot more un burnt fuel is going through now with 2bular manifold and decat.
Exactly the same thing happened to me, which is why I started the thread