Check if folder exist

Hi I'm trying to check if a folder exist and if not create
the folder. I have the code below but I keep on getting an
error "an object could not be found".

Set f5 = f4.Folders(mfolder) 'this works
Set f6 = f5.Folders(mr_number) 'this blows up
If f6 Is Nothing Then
f5.Folders.Add (mr_number)
End If

Anybody can help?

Thanks,
Jay