VBA GetWorkbook for open or not open files w/ error handling

' Reuses a workbook if it's already open, else opens it.
' This function prevents "Automation Errors" that happened to me
' in Excel 2017 when I used "On Error Resume Next" instead of
' "proper" error handling.
'
' WARNING: translated and adapted without testing. May need rounding out.
Function GetWorkbook(ByVal sPath As String, ByVal sFileName As String) as Workbook
Dim wb as Workbook
Dim sFullName As String
Dim erro As Boolean

    sFullName = sPath & sFileName ' sPath has trailing \

    On Error GoTo erro:
    Set wb = Workbooks(sFileName)
    On Error GoTo 0

    If Not erro Then
        ' File is already open. Let's check if it's the right one.
        If wb.FullName <> sFullName Then
            ' Uh oh, it doesn't match the desired path.
            Call MsgBox("Open workbook has wrong path.", vbCritical)
            End
        End If
    Else
        ' We may have gotten here by an error, so let's reset our error flag.
        erro = False
        On Error GoTo erro
        Set wb = Workbooks.Open(sFullName)
        On Error GoTo 0

        If erro Then
            ' Couldn't open. Probably 404.
            Call MsgBox("Couldn't open workbook. Check the path.", vbCritical)
            End
        End If
    End If

    Set GetWorkbook = wb

    Exit Function

erro:
    erro = True
    Resume Next
End Function