When trying to update FBACKUP.EXE from 18.104.22.1680 to version 4.8.275, the following message appears:
"... DeleteFile failed; code 5
When receiving such a message, you need to make sure the fbackup.exe process is not running.
After that you can double click the the FBackup setup file to start the installation.
Usually that message appears with a retry or abort option.
If the popup is not closed, you can press retry after stopping the above process.