The code you have written in cmbBatchno_TextChanged event is that if the value selected in cmbBatchno(combobox) matches with the number from retrieved data, then it will disable the textbox.
see your code
if (cmbBatchno.Text == dtBatchNoDtls.Rows[i]["BatchNo"].ToString())
{
txtExpdate.Enabled = false;
txtMRP.Enabled = false;
break;
}
you have written
txtExpdate.Enabled = false;
which disables the textbox. if you want that the textbox should not be disabled then make it true instead of false in if condition. like this
txtExpdate.Enabled = true;
Any help needed plz reply.