i have a form, which is used to mark students work, each student has an id (upn) and each test has an id and to comment on the students performance on the test, the teacher enters a comment which is linked by test and student id. this is because the same student can do different tests and have different comments and different students can do the same test and have the same comments.. does anyone know how i can work around this error

con4.ConnectionString = "PROVIDER=Microsoft.Jet.OLEDB.4.0;Data Source = f:\Docs\College\Computing\CW\Form\VB Forms\VB Forms\Database Design.mdb"
con4.Open()
sql4 = "SELECT [Comments].Comment FROM [Comments] WHERE [Comments].UPN = '" & upnpass & "' AND [Comments].TestID ='" & idpass & "';"
da4 = New OleDb.OleDbDataAdapter(sql4, con4)
da4.Fill(ds4, "info")
con4.Close()
maxrows4 = ds4.Tables("info").Rows.Count
commentbx.Text = ds4.Tables("info").Rows(inc4).Item(0)