The listing returned by OpenFolderListing only contains the immediate children of that folder. This means that if the folder only directly contains other folders, you will just get those folders back. If you want to get the documents contained in the folder and all of its subfolders you have two options: 1.) Recurse through all of the subfolders returned by OpenFolderListing or 2.) Use a search object instead of manually going through the folders. I would recommend option 2; the server provides search functionality for a reason! The syntax for the appropriate search would be

{LF:LOOKIN="myFolder"}