Connect to the OBDII cable under the seat with an OBDII reader, TuneECU on your laptop or take it to your dealer. I know AutoZone and other auto parts stores will read it for free as well.
while doing the mods did you have to disconnect any of the Plugs under the tank as if one s not quite plugged in properly it make be causing an intermittent connection and while it may not stop the bike running it could be enough to throw an error back to the ECU.
I would be tracing back all connections you disconnected and make sure they are seated properly also any wires that may have been pulled tight should also be checked it could quite possibly just be one of several Sensors located around the bike.
I would be check these while waiting for the cable to arrive then using TuneECU will allow you to read the Error code (a list of codes is in the Workshop manual) and clear it, this is a link to getting the cable http://www.lonelec.co.uk/index.php?main_page=product_info&products_id=32