Thank you for your post.
With the information provided, it is difficult to determine what is the problem. Obviously, something changed.
Let's assume something went wrong with FileMaker Server. Therefore stop all databases and stop FileMaker Server. Then, I would reboot the machine (which will also refresh the operating system). Relaunch FileMaker Server and see if the database files are now accessible via IWP. If this works, then be sure to keep on eye on this over the next couple of days.
If this doesn't work, then I would uninstall FileMaker Server and reinstall it. This will write fresh files. It will NOT overwrite your database files. Deploy the server, open the database files, and see if the file(s) can be accessed via IWP.
Let's start with this, and depending on the outcome, I'll know what steps to take next.
Any chance someone changed your firewall settings when you weren't looking? Checking those might be less laborious than re-installing FM server.
Thank you for your suggestions ..will try them today. :)