I put resume (plus some additional code) in the error handler and that cleared up the first issue if symbol is not found in column A. Still having trouble if the user enters and invalid date in column B (e.g. enters a Saturday, Sunday, holiday, etc). Not sure if I need another resume someplace in the code and I am just not seeing it.

Option Explicit

Private Sub CommandButton1_Click()

    Application.ScreenUpdating = False
    
    Dim HSDFY As HistoricalStockDataFromYahoo
    Dim rs As ADODB.Recordset
    Dim i As Long
    Dim j As Integer
    Dim lastrow As Integer

    On Error GoTo Err_CommandButton1_Click
    
    Range("C2:D" & Rows.Count).ClearContents

    i = 2

    lastrow = Range("A" & Rows.Count).End(xlUp).Row

    For j = 2 To lastrow
        Set HSDFY = New HistoricalStockDataFromYahoo
        Set rs = HSDFY.GetHistoricalData(Cells(j, 1).Value, Cells(j, 2).Value, Cells(j, 2).Value)
        rs.MoveFirst
        Cells(j, 3).CopyFromRecordset rs
        i = i + 1
    Next j

Exit Sub

Err_CommandButton1_Click:
    Select Case Err.Number
        Case 10000
            MsgBox Err.Description
            j = j + 1
            i = i + 1
            Resume
        Case 10001
            'invalid interval
            MsgBox Err.Description
            j = j + 1
            i = i + 1
            Resume
        Case 10002
            'query failed
            MsgBox Err.Description
            j = j + 1
            i = i + 1
            Resume
    End Select
    
    Application.ScreenUpdating = True
    
End Sub