With show hidden files set there was no "garbage name" file listed. I reran Eraser and the garbage name file showed. After I deleted the file, drive C still shows 91.7 MB free of 583 GB with no garbage name file listed. What next?
I can email screen shots if needed.
If the same unused space erase task is still there, right-click, view task log and select the session in which it left with reduced space. Scroll to the end and see what were the last 10 errors or so. Please copy and paste them here.
If you started the task from the context menu, and it completed normally, there will be no task entry in the schedule. If the Task list has been cleared because of an error, there should have been some sort of error dialog.
Are there any folder names in the root of the target drive that you don't actually recognise?
Another possibility is a pre-existing issue with the file system before you ran Eraser. Could you run check disk on the target drive? As it's the system drive, Windows will probably ask to do the check on reboot.