what is the error in it

See more:

C#

hi

OleDbConnection con = new OleDbConnection("provider =Microsoft.JET.OLEDB.4.0;data source=D:\\connect\\customer.mdb");
                con.Open();
               OleDbCommand cmd = new OleDbCommand("Insert into add values('"+nametxt.Text+"','"+emailtxt.Text+""+comboBox3.SelectedItem.ToString()+"','"+religiontxt.Text +"','"+dobtxt.Text+"','"+languagetxt.Text +"','"+mobiltxt.Text+"','"+statetxt.SelectedItem.ToString()+"','"+citytxt.SelectedItem.ToString()+"','"+areatxt.Text+"','"+strtxt.Text +"','"+htxt.Text +"','"+pintxt.Text +"','"+landtxt.Text +"','"+snametxt.Text +"','"+dobtxt1.Text +"','"+wedtxt.Text +"','"+cnametxt.Text +"','"+dobtxt2.Text +"','"+cnametxt1.Text +"','"+dobtxt3.Text +"')", con);
               // OleDbCommand cmd = new OleDbCommand("Insert  into add values('s','a','a','a','a','a','a','a','a','a','a','a','a','a','a','a','a','a','a','a')", con);
               cmd.ExecuteNonQuery();
                MessageBox.Show("Added " + nametxt.Text + " as your customer", "Information", MessageBoxButtons.OK, MessageBoxIcon.Information);
                con.Close();

what is the error in the connection it was showing as
"Object reference not set to an instance of an object." the access2003 database contains 20 fields

for i am wasting nearly one hour fo rthis simple thing but i dont know what is he reason

please help me