I have been able to demonstrate that unattended backups do not work in FBackup 4.6 build 255, an equivalent job does however work in the Backup4all professional on the same system, same account.
Operating System is Windows 7 Home Premium
Please let me know if you plan to address this, I am prepared to provide all of the details of the setup, and help validate that the bug is fixed if need be. I did notice significant security setup differences in the files and folders between the installs, but have not had time to see if that is the root cause of the issue.