Dave,
I had the same message recently, turns out I accidently loaded the wrong lights with the LN process, I read a tutorial which suggested storing the LN files in the same folder as the Registered Lights (one shot colour for me), that way you cant make a mistake like this.
For you, if your not already doing it, Have separate folders for L, R, G, B & Ha registered images, when running LN on them choose the same destination folder which your 'Red' lights are in, same with your drizzle files. So, for example, all your 'Red' registered Lights, all you 'Red' LN files and all your 'Red' drizzle files all reside in the same folder.
When it comes to the final integration, load up all your 'Red' registered lights, when loading your L Norm files they will be in the same folder as will your drizzle files.
Took me a couple of hours to work out that I did actually use my original Light subs for the L Norm process LOLOL Easy done
Regards
Paul