Error I am getting: Child list for field prc_GetBomLinePartsDetail cannot be created.

I have two datasets or two tables that are related.  Table A is Parent, Table B is the child. I may be getting this error because the table B child table has not bill fill.

this.gridDataSource =this.tableATableAdapter1.GetData(tableAdetails); 
this.ultraGrid1.DataSource = this.gridDataSource;

 foreach (var Row in ((DataSet.tableADataTable)this.ultraGrid1.DataSource)) // I get error on this line
 {

      I am trying to fill or table B child table base of the table A parent table ID. Im basically looking for relation parent ID in the table B child table and fill as If ID exists

if (!Row.IsIDNUll())
{
   string wiirId = Row.ID.ToString();
    this.tableATableAdapter.Fill(this.DataSet.tableA, Id);
   this.tableBTableAdapter1.Fill(this.DataSet.tableB, Id);
   this.ultraGrid1.DataSource = this.DataSet;
}

 }