Did you rinse the Rockwool before use, with properly ph'd water?
What's the ph of the water you're using?
Are you keeping the Rockwool damp, or have you let it dry out between waterings?
Why are you starting in Rockwoll, then putting them into soil? Why not germinate 'em in a bleach-free paper towel? (cheaper and quite effective)

Some seeds covers are stubborn hard, and may need coaxing to germinate. A gentle scuffing with 180 or 220 sandpaper will allow easier access for the moisture to enter the seed.