Krisp, Let's start by trying to narrow down the problem. Does it work if you comment out the call to the DAO? If not, we can rule out the DAO. Does it work if you pass null as the VO? If not, the problem is in the VO.
Jeanne, i did not comment out the call to DAO, instead i used the codes in DAO in my Action. It worked perfectly. when i passed null, instead of VO, no exception was thrown out. the code exection was back on track. so can we rule out the parts of DAO and VO.