One or more rows contain values violating non-null, unique, or foreign-key constraints

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when i Click on Print button the Above Exception through RvCustomerBill.Visible = true;

                RvCustomerBill.Visible = true;                 
                Medical.MedicalDBFDataSetTableAdapters.CUSTOMERBILLTableAdapter adapter = new Medical.MedicalDBFDataSetTableAdapters.CUSTOMERBILLTableAdapter();
                MedicalDBFDataSet.CUSTOMERBILLDataTable table = new MedicalDBFDataSet.CUSTOMERBILLDataTable();
                adapter.FillBy(table,txtBillId.Text);
                ReportDataSource ReportSource = new ReportDataSource("CustomerBillReportDataSet", (DataTable)table);
                RvCustomerBill.ProcessingMode = ProcessingMode.Local;
                RvCustomerBill.LocalReport.DataSources.Clear();
                RvCustomerBill.LocalReport.DataSources.Add(ReportSource);
                RvCustomerBill.LocalReport.Refresh();
                RvCustomerBill.RefreshReport();