If you can't delete an ISO file as the file is open in your System, check if it is mounted as a drive or not. Uses these proven fixes to resolve the issue.

If you cannot delete a file or a folder on an NTFS file system volume in Windows, follow the solutions mentioned in this post to resolve the issue.

Why Cant I Delete, Edit, or Rename a File That Is in Use? Windows prevents you from deleting, moving, or renaming files that are in use to keep your computer system stable.

Files aren't stuck open since I restarted the server. It was a file server where someone dumped stuff. The user in question left long ago so it was time to delete all her junk.