B100A-15 code

Just done the 10 yr service on the old girl, well old might be exaggeration, she comes into her teens in December, anyways did the timing, auxiliary belts, new pulleys, tensioners, water pump, general service, came to start her up, won't start click click , put the gap tool on to her the dreaded B100A-15 code popped up, panic ensues, but but it started when I prime the diesel filter. Why won't it work now, mutter mutter, then looked at some of the other codes that came up, something about a low battery, uhmmmm connected a spare battery up, she lives hurrar , code is still there but that is there for another day, seems to be quite the mystery this B100A-15. Moral of the story .... keep your battery on charge when starting car after priming filter.