can anyone explain this error?

Private Sub btnAddDoc_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAddDoc.Click
    If txtDocID.Text = "" OrElse txtDocName.Text = "" OrElse txtDocType.Text = "" Then

        lblNotice.Text = "PLEASE COMPLETE ALL THE REQUIRED FIELDS!!!"
    Else
        If btnAddDoc.Text = "Add Document" Then
            Dim connstring As String = "Provider=SQLOLEDB;Data Source=RONALDAMIT-PC;Integrated Security=SSPI;Initial Catalog=UEP Document Logbook"

            Dim conn As New ADODB.Connection()
            conn.ConnectionString = connstring
            conn.Open(Nothing, Nothing, Nothing, -1)

            Dim rs As New ADODB.Recordset()

            Dim sql As String = "Insert into AddDocument (DocID,DocName,Doctype) values ('" + txtDocID.Text + "', '" + txtDocName.Text + "', '" + txtDocType.Text + "')"

            rs.Open(sql, conn, ADODB.CursorTypeEnum.adOpenStatic, ADODB.LockTypeEnum.adLockReadOnly, -1)

            MessageBox.Show("Document Added")
        End If
    End If
End Sub>