Thank you for your post.
Have the users select "Open Remote" from the File menu and enter the IP address and file name manually. Are they then able to access the file? If so, then double-check the icon and make sure the script being used is opening the correct file.
If it still doesn't work, then make sure the Admin Console is responding. If not, then you may have to reboot the server.
Any other information you can provide may be helpful.
If you could also post your crash log it may help figure out what the issue may be.
You can find the one that pertains to FileMaker in the /Users/<user>/Library/Logs/CrashReporter/
It should say something like com.filemaker...
Just to note, be sure not to back up the live file that is being hosted, but to save a backup copy.