Upgrade to FW 5.11, no Web interface.
Make a reset, nothing change. Erase own files, still no web interface. In fact, could not even connect to laptop through LAN cable, only through USB cable.

Downgrade to FW 5.10, Web ok (as before the upgrade).

Upgrade again to FW 5.11, again no Web interface. But this time I could connect through LAN cable from my laptop.
Make a reset and erase own file from Web site, still no Web interface, but still able to connect to my laptop through LAN cable.

Downgrade to FW 5.10, Web ok again.

All results were regardless I was using PLC 5.1.1.2 or 5.1.0.0.

No error message through the upgrade.
Must be some kind of bug.