Fatal error encountered during command execution.错误

运行后出现这个错误，怎么回事啊
public void SelectDatas(string tasktableid,int toid)
{
Task task = new Task();
StringBuilder sa = new StringBuilder();
sa.Append("select datas");
sa.Append(" from t_taskdatas,t_taskdata");
sa.Append(" where t_taskdata.taskdataid=t_taskdatas.taskdataid and t_taskdata.tasktableid=@tasktableid and t_taskdatas.upid=@toid");
MySqlParameter[] pmts = new MySqlParameter[2];
pmts[0] = new MySqlParameter("@tasktableid", tasktableid);
pmts[1] = new MySqlParameter("@upid", toid);
DataTable dt = DB.getDataTable_Pmts(sa.ToString(), pmts);
foreach (DataRow dr in dt.Rows)
{
task.datas = dr["datas"].ToString();
aList.Add(task);
}
}
这是查询代码，我在数据库里输入上面的SQL语句都可以查出来，可是程序里就总错误，求指点