If you take this file back down off the server, open it with FileMaker Pro and choose Sharing | FileMaker Network from the File Menu, what do you see?
Make sure that "All Users" is selected in "network access to file" when you select this file in the "currently open files" list on the left.
If that isn't the issue, can you see any hosted files on this server?
If no files are listed, you may be dealing with this bug:
For More Information see:
This is one of many acknowledged bugs that can be found in the Known Bug List 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