Well, I get mine up to 75% or higher, so I doubt that is what killed them, unless your humidity was too high during incubation. The real art to hatching is that its a bit different for every location.
If you live in a high humidity area, you'll want to strive to keep it lower, and be sure to monitor weekly that your eggs are losing sufficient moisture weight to allow ample oxygen and space in their egg for turning and breathing. If you live in a lower humididy place, you'll want to keep it a tough higher,, and really raise it at the end. If you live where it's perfect (25-35% during incubation) you won't want to add much moisture at all, but you will add it for lockdown.
It is quite usefull to get a paper and monitor your temps and humidity for every hatch, noting bird type (chicken,turkey, duck, goose, quail, guinea, pheasent, etc) and a daily log of humidity. You might find that at one humidiy and temp you get a better hatch, then you'll know whats best for your area for that season. I have to add more water in early spring, and less in summer hatches. I have to mark my air lines on eggs at set, and weekly after to monitor air increase (and thus water weight loss). If it's not gaining air space, I drop humidity. If the air space is getting too big too quick, I add more moisture in the forms of wet sponges usually. A few hatches, and you'll have this down to an art form yourself.
