folder names not showing in list view

I am having trouble with folders in a portfolio (Acrobat X Pro). The file names are there and all look fine in X Pro, but when my users view it in Reader 9, the file names are missing in the List View. In the layout view, the folder names are there as you scroll through. What did I do wrong? The wierdest thing is that of the 10-12 folders I created, ONE folder's name does appear in the list view. I can't imagine what I did differently with that one. I so appreciate any help on this! Thanks!