Why getting an error when click a checkbox

I am getting an error...  "Argument not optional" when I click on a checkbox to make it true.  The onclick code is:

Private Sub chkbxTranscriptionComplete_Click()

    If Me.chkbxDataComplete = True Then
       If MsgBox("An email will be sent to the assistant to let them know the data has been completed.  Do you wish to continue?", vbYesNo + vbQuestion + vbDefaultButton2) = vbYes Then
            SendEmailOutlook "somebody@somewhere.com", "Data Complete" & " - " & Me.txtFirstName & " " & Me.txtLastName, "The data has been entered for " & Me.txtFirstName & " " & Me.txtLastName & ". "
       End If
    End If

End Sub

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And the module code to send the email is:

Public Sub SendEmailOutlook(strTo As String, strSubject As String, strBody As String, _
    strFile As String, Optional bFileAttach As Boolean = False, Optional bPreview As Boolean = False)
    
    On Error GoTo SendEmailOutlookErr
    
    Dim strEmail As String
    Dim strMsg As String
    Dim oLook As Object
    Dim oMail As Object
    
    Set oLook = CreateObject("Outlook.Application")
    Set oMail = oLook.createitem(0)
    With oMail
        '.ReplyRecipients.Add "ben@accessdatabasetutorial.com"
        .to = strTo
        '.body = sBody
        .htmlbody = strBody
        .Subject = strSubject
'        If strFile <> "" Then
'            .Attachments.Add (strFile)
'        End If
'        If bFileAttach = True Then
'            'THIS IS WHERE YOU CODE YOUR FORM TO ATTACH FILE(S)...
'            '.Attachments.Add (CurrentProject.Path & "XYZ.XXX")
'        End If
        If bPreview = True Then
            .display
        Else
            .Send
        End If
    End With
    
    If bPreview = False Then
        Set oMail = Nothing
        Set oLook = Nothing
    End If
    Exit Sub
    
SendEmailOutlookErrExit:
        Exit Sub
    
SendEmailOutlookErr:
        MsgBox Err.Description, vbOKOnly, Err.Source & ":" & Err.Number
        Resume SendEmailOutlookErrExit
End Sub

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