Bars Suck
Keep in mind that in general, bars suck, but sometimes that's all you've got. Almost all use "hydrolyzed protein" or some other similar named filler. This is basically gelatin which is made from ground cow hooves. Its not the kind of protein you are looking for, but when analyzed at the lab, it does include the nitrogen (I believe) content of a protein and is therefore counted in the protein total for the bar. Jell-O doesn't claim any protein on their label, but they aren't trying to sell a protein product.
The other popular "gotcha" is glycerin. It is used as a filler to keep the bar moist and hold it together. Each gram of glycerin has about four calories. From what I have read, it is basically a simple carb, but the FDA does not (yet) require it to be labeled as such. The problem here is that it would significantly raise the carb level of otherwise lo-carb bars. This is usually where all of the other calories are when you subtract protein, carbs & fat from the calorie total.
B-Mac