How to solve problem with datagrid and tabcontrol

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VB

Good day,

I created a tabcontrol that has more than two tabpages, in each of the tabpages, i have a datagrid except the first page.
I have populated the datagrid successfully. The problem is when i click to view the 2nd tab page, the content of the datagrid will display well but on the 3rd tabpage, the content of the datagrid will not be visible (the text is white in color), that is the datagrid on the 3rd tabpage will be populated with data but the content is white in color thereby it's kinda invisible.

here is my code:

tab click event:

Private Sub TabControl1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TabControl1.SelectedIndexChanged


        If TabControl1.SelectedIndex = 5 Then

            'load symptoms
            loadSymptomsCmb()

            'load patient diagnosis history
            loadDiagnosisHistory(mqhModule.treatPatID)


            'show doc name
            txtDoc.Text = mqhModule.docName

        ElseIf TabControl1.SelectedIndex = 6 Then


            'load prescription history
            loadprescription(mqhModule.treatPatID)

            'load drugs
            loadDrugsCmb()

            'show doc name
            txtDrugsBy.Text = mqhModule.docName

        End If

    End Sub

code to populate datagrid:

Private Sub loadprescription(ByRef patID As String)



        Try
            'retrieve patient info
            'retrieve patient info

            'open database
            conMod.openDB()


            'get first student name list from database

            Dim StrSQL As New SqlDataAdapter("SELECT drugs,medicine,dura,dosage,freq,drugInstruction " & _
                                                "presTime,presDate,prescribeby " & _
                                             " FROM patientprescription WHERE patientID='" & patID & "'  ", conMod.Con)

            Dim DR As New DataSet

            StrSQL.Fill(DR)
            StrSQL.Dispose()

            Dim usertable As DataTable = DR.Tables(0)




            'datasource of the datagrid
            DGridPres.DataSource = usertable



            'change the data grid column name
            DGridPres.Columns(0).HeaderText = "Medication"
            DGridPres.Columns(1).HeaderText = "Drug"
            DGridPres.Columns(2).HeaderText = "Duration"
            DGridPres.Columns(3).HeaderText = "Dosage"
            DGridPres.Columns(4).HeaderText = "Frquency"
            DGridPres.Columns(5).HeaderText = "Instruction"
            DGridPres.Columns(6).HeaderText = "Time"
            DGridPres.Columns(7).HeaderText = "Date"
            DGridPres.Columns(8).HeaderText = "Prescribed-By"



            'close database
            conMod.closeDB()

            'catch exception
        Catch ex As Exception

            'dsplay message
            Dim mymsg As New myMsgbox

            With mymsg
                .txtError.Text = "Error! Could not retrieve Patient prescription Information."
            End With

        End Try


    End Sub