Prevent import from happening more than one time

Private Sub cmdImportAndClean_Click()
On Error GoTo Err_cmdImportAndClean_Click

    If IsNull(Me.FileList) Or Len(Me.FileList & "") = 0 Then
        MsgBox "Please select an Excel file."
        Me.cmdCancel.SetFocus
        Exit Sub
    End If

    If MsgBox("This function will import the Excel file you have selected into the Participants table. Do you want to continue?", vbYesNo + vbQuestion + vbDefaultButton2) = vbYes Then

    Dim db As Database
    Set db = CurrentDb
    db.Execute "delqryDeleteRecordsFromtblTempParticipantImport", dbFailOnError

    DoCmd.Hourglass True

    DoCmd.TransferSpreadsheet acImport, acSpreadsheetTypeExcel9, "tblTempParticipantImport", Me.FileList, True

    Dim tblDef As TableDef
    For Each tblDef In CurrentDb.TableDefs
    If InStr(1, tblDef.Name, "ImportError") > 0 Then
        DoCmd.SelectObject acTable, tblDef.Name, True
        DoCmd.DeleteObject acTable, tblDef.Name
        Beep
    End If
    Next tblDef

    db.Execute "apndtblqryImportParticipantRecords", dbFailOnError

    Else

    MsgBox "Import Function Cancelled"

    DoCmd.Close , "frmBrowse", acSaveNo

    End If

    MsgBox "The import file was successfully imported."

    DoCmd.Close acForm, "frmBrowse", acSaveNo

    DoCmd.Hourglass False
 
Exit_cmdImportAndClean_Click:
    Exit Sub
    
Err_cmdImportAndClean_Click:
    MsgBox Err.Description
    Resume Exit_cmdImportAndClean_Click
 
End Sub