There are many reasons why the eggs might have been infertile.
1. Was the female (and/or male) brumated prior to breeding?
2. First time male and female may not have been sexually mature.
3. Did she have an appropriate lay box so that she laid them on time and wasn't holding them inside of her too long?
4. Were they slugs when she laid them or did they go bad during incubation?
There a dozens, or more, reasons why eggs may not hatch. Please give us more information about that breeding so we can help.