"More than One Message or Notes Control" error in VBA when creating Outlook mail item.

Automating Outlook from within Excel (2016) using VBA, I'm using fairly standard code to create a new mail object, set the To, Subject, Attachments, and Body, and display.

On Error Resume Next
Set oOutlookApp = GetObject(, "Outlook.Application")
If Err <> 0 Then
    Set oOutlookApp = CreateObject("Outlook.Application")
End If

Set oItem = oOutlookApp.CreateItem(olMailItem)

With oItem
    .To = tostring
    .Subject = "Project Field Schedule: " & skeddeets.Cells(3, 2) & " " & skeddeets.Cells(3, 4)
    .Attachments.Add savedname
    .Body = "Attached please find the latest Field Schedule for the " & skeddeets.Cells(3, 2) & " " _
    & skeddeets.Cells(3, 4) & " project." & vbCrLf & vbCrLf & vbCrLf
    .Display  '.Send
End With

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Sometimes it works fine, but about half the time I get this error message:

When I dismiss the error a looking at the new mail item, I can in fact see multiple redundant fields in the new email "form."  And I can't edit the body or send the email.  Where did these 'ghost' fields come from?  I've never seen these when I create a New Email from within Outlook.  How can I fix this error?  Thanks!