Thank you for your post, and I apologize for the late reply.
My first thought is that the DSN is not set up properly on Server. From FileMaker Pro client, open the file being hosted on Server, pull down the File menu and select Manage -> External Data Sources. Although you initially set this up on your local machine, verify the path or reset it for the Server machine.
If you are continuing to have difficulty, let me know what actions you have made on the Server.