I am testing CustomReportJob with Sandbox and I always have the same xml returned. The columns are always the same and there are no rows. What's the problem?

<?xml version="1.0" standalone="yes"?><report><table><columns><column name="campaign"></column><column name="adgroup"></column><column name="agStatus"></column><column name="imps"></column><column name="clicks"></column><column name="ctr"></column><column name="cpc"></column><column name="cost"></column><column name="pos"></ column></columns><rows></rows></table><totals><grandtotal imps="0" clicks="0" ctr="0.0" cpc="0" cost="0" pos="0.0"></grandtotal></ totals></report>