Are you using Open Remote to access files already opened with Filemaker Pro on the host computer?
DHCP settings should have no effect on their ability to find and connect to such a hosted file.
If you have the files stored in a shared directory and users are navigating directly to the shared file to open it, then you run a very real risk of corrupting your database files.
The files are being served by Filemaker Server V11. I access the files using filemaker open remote to get to the files. The clients see the server but don't see the files. The client with the most problem used to be the server machine. I uninstalled the server and I am now thinking that was not enough. I am in the process of wiping the machine completely, installing a fresh system and then filemaker 9 client. I will report back with the results.
Here is one possibility (This is the link for the Mac version of this bug): Can't login to FMS database on new Mac, other Macs can
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