Thank you for your post.
Unfortunately, we no longer support FileMaker version 5, so that may be the reason why no one has responded.
If you have 45 files being hosted, and only one has this problem, then something has told FileMaker Server this file cannot be shared. My gut feeling is that you would need to reboot. You may want to let everyone know that the machine will be taken down for a brief maintenance at a certain time so everyone can be prepared for this. Also, try to do it when it is the least disruption. Late Evening or early morning hours may be a possibility.