All ok!! I have resolved installing a previous firmware released on 2011 08 04.
This firmwware hasn't flash player inside, so I haven't had problem to install
the newest version of flash player (v.10.3.186.7).
I suggest everyone to install this release and test (for me it's ok) and then,
for a 1080p HDMI output, I suggest also, to install Hdmiswitch.
The link for this firmware is: http://www.geniatech.com/down-eng/Androidtvbox/20110804.zip
(Unzipping file, you'll find two zipped file; the first, update.zip, is for firmware upgrade)
Instead Flash player and Hdmiswitch can be find in:[link removed by moderator]
Thank you szemo77 and HT1 for your advices