Vb net update statement issue - vb.net-2010

Question

I have vb.net project for insert and update values in SQL server.It has sql code as below:
Public Sub insert_customer_new(ByVal customer_id As Integer, ByVal work_state As Integer)
Dim cmd As New SqlCommand("insert into customer_tbl (customer_id , work_state ) values (#customer_id, #work_state )", conn)
cmd.Parameters.Add("customer_id", SqlDbType.Int).Value = customer_id
cmd.Parameters.Add("work_state", SqlDbType.Int).Value = work_state
If conn.State = ConnectionState.Open Then conn.Close()
conn.Open()
cmd.ExecuteNonQuery()
conn.Close()
cmd = Nothing
End Sub
And then
Public Sub update_customer_new(ByVal customer_id As Integer, ByVal work_state As Integer)
Dim cmd As New SqlCommand("update customer_tbl set work_state = #work_state where customer_id = #customer_id ", conn)
cmd.Parameters.Add("customer_id", SqlDbType.Int).Value = customer_id
cmd.Parameters.Add("work_state", SqlDbType.Int).Value = work_state
If conn.State = ConnectionState.Open Then conn.Close()
conn.Open()
cmd.ExecuteNonQuery()
conn.Close()
cmd = Nothing
End Sub
I use form Button.Click Event for insert
Private Sub insert_customer_Click(sender As Object, e As EventArgs) Handles insert_customer.Click
If customer_id.Text = String.Empty Then
MsgBox("Pleas Enter Customer Number")
customer_id.Focus()
ElseIf state_txt.Text = String.Empty Then
MsgBox("Pleas Enter The Start State Number ")
state_txt.Focus()
Else
insert_customer_new(customer_id.Text, state_txt.Text)
MsgBox("Insert Done !")
End If
End Sub
And by same way I use form Button.Click Event for update
Private Sub update_state_Click(sender As Object, e As EventArgs) Handles update_state.Click
If customer_id.Text = String.Empty Then
MsgBox("Pleas Enter Customer Number For Update")
customer_id.Focus()
ElseIf state_txt.Text = String.Empty Then
MsgBox("Pleas Enter The New State Number ")
state_txt.Focus()
Else
update_customer_new(customer_id.Text, state_txt.Text)
MsgBox("Update Done !")
End If
End Sub
The problem is some time the update statement does not perform. It gives no error, and the Procedure just skip this line for unknown reasons.
And it's happened about 10% of all cases that performed after application is published.