Detect missing fonts in a powerpoint 2007 document

[Johnson]

I try to detect the missing font in a powerpoint 2007 by the following VBA
code:

For Each usedFont In Presentations(1).Fonts
If usedFont.Embedded Then
MsgBox usedFont.Name & ": Embedded"
Else
MsgBox usedFont.Name & ": Not embedded"
End If
Next usedFont

but an exception occurs while executing the code "usedFont.Embedded".

Thanks in advance!