TOS 4.2.12 - FTP Services doesn't start

[giudest]

TOS 4.2.12 - F2-210
is not possible to enable ftp service from web GUI.
After checked it, the GUI shows "saved" but the check box is blanked and the service doesn't start.

The SFTP service is ok and running fine.
The FTP service was good with the TOS 4.2.8

[TMS]

You can clear the browser cache, if it still fails to start, reinstall the system.