Could be several things.... some questions first.

- is it getting too much water?
- is the soil well draining (this is very important)
- are all the fronds getting yellow or just the older ones? If the lower, older ones, this could be just transplant stress.

- when you planted it, did you just move it from the pot to the hole or did some of the soil fall away from the roots? I find that they go through less stress if just moved from pot to new location without removing soil. I also find that ammending the soil to be as much like the soil that the palms came in, really help to reduce stress and augements growth.

???