I have tried almost everything, and nothing works. I have this code in button event, on the first click datagridview is populated from database, and on the second click database should be updated from datagridview. That last part doesn't work. Just to mention that changes are made in datagridview in between click through mouse click event (click on cell inserts a value).

Dim ConnString As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=w:\PD_Z.mdb"
            Dim SQLString As String = "SELECT * FROM ZARADE"
            Dim OleDBConn1 As System.Data.OleDb.OleDbConnection = New System.Data.OleDb.OleDbConnection(ConnString)
            Dim DataSet1 As New DataSet()
            Dim OleDbDataAdapter1 As System.Data.OleDb.OleDbDataAdapter = New System.Data.OleDb.OleDbDataAdapter(SQLString, OleDBConn1)

            If Button2.Text = "Unos podataka" Then
                OleDbDataAdapter1.Fill(DataSet1, "ZARADE")
                DataGridView1.DataSource = DataSet1.Tables("ZARADE")
                DataGridView1.ReadOnly = False
                Button2.Text = "ZAVRSI UNOS"
                Button2.ForeColor = Color.DarkRed
                Button1.Enabled = False
                Label4.Text = "Dok je opcija <ZAVRSI UNOS> aktivna, podaci iz tabele se klikom mogu menjati"
                Label4.ForeColor = Color.DarkRed
                ComboBox1.Enabled = False

                Using con = New OleDbConnection(ConnString)
                End Using

                Label4.Text = " "
                Label4.ForeColor = Color.Black
                'DataGridView1.ReadOnly = True
                Button2.ForeColor = Color.Black
                Button1.Enabled = True
                ComboBox1.Enabled = True
                'Dim cb As New OleDbCommandBuilder(OleDbDataAdapter1)
                '  cb.QuotePrefix = "["
                '  cb.QuoteSuffix = "]"
                '  OleDbDataAdapter1.Update(DataSet1.Tables("ZARADE"))

            End If
Now I am getting this error : "Value cannot be null, Parameter name : dataTable"