Subject: I suspect that the DateOnly portion of the NDT is empty
Are there any similarities between the machines that the error occurs on? Specifically looking for information on Notes version, OS, OS Locale.
You could work around the error with this code
Dim auxdate As New NotesDateTime("")
If Cstr(auxdate.dateonly) <> "" Then
Print "Cdat", Cdat(auxdate.DateOnly)
Else
Print "Datenumber", Datenumber (Year(auxdate.LSLocalTime), Month(auxdate.LSLocalTime), Day(auxdate.LSLocalTime))
End If