Can someone help me take a look with my code

I develop a program to add data from combo box and delete data from combo box. i will get error when i delete too many time data from database below is my code.

delete data from combo box

If cnn.State = ConnectionState.Open Then
            cnn.Close()
        End If

        Dim da As New OleDbDataAdapter
        Dim dt As New DataTable

        If txtCONDITION_NAME.SelectedItem Is Nothing Then
            Return
        Else
            If Not cnn.State = ConnectionState.Open Then
                cnn.Open()
            End If
            cmd.Parameters.Clear()
            Using cmd = New OleDbCommand()
                cmd.Connection = cnn
                cmd.CommandText = "DELETE FROM tbl_ConditionName WHERE ConditionName = @ConditionName;"
                cmd.Parameters.AddWithValue("@id", txtCONDITION_NAME.SelectedItem)
                cmd.ExecuteNonQuery()
            End Using
            MessageBox.Show("Record Is Deleted")
            da.SelectCommand = New OleDbCommand("select * from tbl_ConditionName", cnn)
            da.Fill(dt)
            txtCONDITION_NAME.DataSource = (dt)
            txtCONDITION_NAME.DisplayMember = "ConditionName"
            txtCONDITION_NAME1.DataSource = (dt)
            txtCONDITION_NAME1.DisplayMember = "ConditionName"
            RefreshData()
        End If

this is my combo box add data code

If cnn.State = ConnectionState.Open Then
            cnn.Close()
        End If

        Dim da As New OleDbDataAdapter
        Dim dt As New DataTable
        cnn.Open()

        Try
            Dim codinsert As New OleDbCommand
            codinsert.Connection = cnn
            codinsert.CommandText = "INSERT INTO tbl_ConditionName ([ConditionName])" &
        "VALUES('" & Me.txtCONDITION_NAME.Text & "')"

            'Trim'
            If txtCONDITION_NAME.Text.Trim = "" Then
                MessageBox.Show("Please Insert Data", "Error Message")
                Exit Sub
            End If
            'Trim'
            codinsert.ExecuteNonQuery()
            MsgBox("Save data successful", MsgBoxStyle.Information, "Message")

        Catch ex As Exception
            MsgBox(ex.Message.ToString)
        End Try

        da.SelectCommand = New OleDbCommand("select * from tbl_ConditionName", cnn)
        da.Fill(dt)
        txtCONDITION_NAME.DataSource = (dt)
        txtCONDITION_NAME.DisplayMember = "ConditionName"

        txtCONDITION_NAME1.DataSource = (dt)
        txtCONDITION_NAME1.DisplayMember = "ConditionName"

        Me.btnClear.PerformClick()
        cnn.Close()

thanks a lot