The following should fix it. I will investigate the error log issue.
Code:
Sub Resize(oDoc As Document)
Dim lngOrient As Long
lngOrient = oDoc.PageSetup.Orientation
If oDoc.PageSetup.PaperSize = wdPaperLetter Then
oDoc.PageSetup.PaperSize = wdPaperA4
oDoc.PageSetup.Orientation = lngOrient
End If
End Sub