We can help better if we have more details:
- Is this a front or rear wheel? Rear wheels sometimes use shorter spokes on the drive side to help with wheel dish for the cassette/freewheel
- What spokes were on the wheel already? Are the butted spokes a direct replacement?
I've had new spokes and nipples separate with aluminum nipples and cheap plain gauge spokes. I used a different nipple and it worked out.