Just remove the
comboBox1.DisplayMember = "";
and replace Table.P_Namee" with P_Name".
Try this,
public void fetchProduct()
{
da = new SqlDataAdapter("Select Prod_Name from tblProdMaster", con);
DataSet ds = new DataSet();
comboBox1.DataSource = ds;
da.Fill(ds);
comboBox1.DisplayMember = "Prod_Name";
comboBox1.ValueMember = "Prod_Name";
}
public void fetchParty()
{
da = new SqlDataAdapter("Select P_Name from tblPartyMaster", con);
DataSet ds1 = new DataSet();
da.Fill(ds1);
comboBox1.DataSource = ds1;
comboBox1.DisplayMember = "P_Name";
comboBox1.ValueMember = "P_Name";
}