It means that you think you're gluten-free, but you're not. You're gluten-light. Look for sources of contamination you might be missing. I tend to get hit with barley because labelling laws ignore it. Check BBQ sauces, cereals, and chocolates for malt.
Along that line, my fiance picked up two containers of dry roasted peanuts from the same manufacturer, and noticed that the larger container (even through it was the same brand, flavor, etc) had wheat starch in it, while the smaller did not. Read every label, every time. Lipton started putting barley in their French Onion soup mix, and I figured it out the hard way. :/
Also, do you eat out? It doesn't matter how careful you are and how particularly people handle your food, restaurants will get you sometimes. If someone handles a sandwich and then handles your food without changing their gloves, that can be enough. The amount needed to have a reaction is smaller than is visible to the naked eye.