The cat missing isn't probably why the light is on. What tune # did you load into it ? Make sure it is one thats designated as "without secondary air injection". That would be map #20363 who's specs are: aftermarket silencers, WITHOUT SAI, all markets except japan. If the bike WITH SAI sees a mpa thats doesn't have SAI enabled it will throw a code and the lite goes on. I assume the other way around is also true, and yours has no SAI. So make sure you re using 20363. Or if you want the bike to be tuned more properly, use the custom decat tune thats available elsewhere. I can't link you to it due to the fact this site won't allow links to the site that hosts the file. But if u PM me and give me your email i'll send it to you. I can't even tell you in a PM because they have the forum code tweaked so if you link to that site even in a PM it shows as a rat forum link instead. Anyways, you'll get better power with it because the triumph tor tunes are not meant for catless running. Your call.....either one will work but the custom tune runs much better.
Oh, and if it's not a incorrect map thats thrown the engine lite, connect tune ecu and look at the bar one the bottom....it will display the error code # that threw the engine light and in the service manual it will tell you what that code means.