[resolved] Error on update

I have a problem in apt-get update, because a public key requested isn’t available; here is the report on sudo apt-get update:
“W: Errore GPG: http://apt.osmc.tv jessie InRelease: Le seguenti firme non sono state verificate perché la chiave pubblica non è disponibile: NO_PUBKEY 553B25A766C762CC”
I I tried to install it from keyserver keys.gnupg.net and a few of other known keyservers, but the key isn’t available. On the command: “gpg --keyserver keys.gnupg.net --recv-key 553B25A766C762CC”
the response is: “gpgkeys: key 553B25A766C762CC not found on keyserver”

If you have problems with the “http://apt.osmc.tv jessie main” key than either something went really wrong on your installation or something is not working inbetween.
Try to upload full logs via grab-logs -A maybe we can spot some issues in the logs.

Exception Details:

Traceback (most recent call last):
File “/usr/bin/grab-logs”, line 783, in dispatch_logs
raise ValueError(‘Upload Returned Empty String’)
ValueError: Upload Returned Empty String

Failed to upload log files, copying to /boot instead. (Unable to verify)

As expected something majorly went wrong with your installation.
My initial thought would be a corrupted SD Card. Suggest to first to a backup if you have anything special on the card and then test the card.
Or maybe it is not the card but internet. So first check if you have the logfiles on your /boot partition.
And maybe try wget http://download.osmc.tv/installers/diskimages/OSMC_TGT_rbp2_20170705.img.gz to check your internet connection

connection and internet are ok. I use my OSMC installed raspberry as mysql server, too, and a couple of other things…
Before to proceed to a complete reinstall, I wish to install only the public key involved, but I didn’t find it, searched everywere

Well if you are so eager to ride a death horse here you go http://apt.osmc.tv/apt.key


Thank You. The issue is gone now!
If someone is interested I proceeded in this way:

wget http://apt.osmc.tv/apt.key
gpg --import apt.key
gpg --send-keys 553B25A766C762CC
gpg --keyserver keys.gnupg.net --recv-key 553B25A766C762CC
gpg -a --export 553B25A766C762CC | apt-key add -

Thank You to fzinken for his help