First, the individual users do not need access to the folder where the hosted files reside. When they use open remote from FileMaker they are linking directly to the host's copy of server and thus do not need direct access to the folder in order to find and open the files.
First, Select Sharing | FileMaker Network... and make sure that sharing is enabled for each file. Click each file listed in the currently open files list and make sure that "all users" is specified. Make sure that the "don't display in open remote file dialog" option is NOT selected.
If you've done all that and still can't see the files listed, check the information in the server admin console help system on ports and make sure all the correct ports are open on the server machine.
If you still can't see the files, this may be the issue:
This is one of many acknowledged bugs that can be found in the Known Bug List thread here in the Report an Issue section of the forum.
It can also be downloaded as a database file from: http://www.4shared.com/file/8orL8apk/FMP_Bugs.html
Got it working, it was the server.pem file on the client. Tried to install on another machine, grab the *.pem, no luck. Tried again with the date set back a year, BAM, Bob's your /* insert relative of choice */