Did you put too much fertilizer in when you planted them? I kilt some marigolds that way once. I think they got fertilizer burn the first time it rained. :(
Didn't put any fertilizer in with 'em at all...though I've fertilized 'em since, just using the Miracle Gro powder stuff that goes in the watering can. But I used the same stuff on the other plants.
Maybe they don't like being overly fertilized, though? And the pansies like more?