040903 A WebService 's method, return value can't be object

I Pay An Answser $ 40 for this error. My God. I Think I can Remeber it for Ever. ^ _ ^

1. This is OK.

[WebMethod] Public DataSet Returnarr () {

DataSet DS = New Dataset ();

......

Return DS;

2.BELOW IS NG.

[WebMethod] public object returnar () {

......

Return DS;