Possible Duplicate: There's an issue with an Alpha/Beta Release of Ubuntu, what should I do? authenticate 'quantal.tar.gz' against 'quantal.tar.gz.gpg' exception from gpg: GnuPG exited non-zero, with code 2 Debug information: gpg: Signature made Fri 28 Sep 2012 03:55:55 AM IST using DSA key ID 437D05B5 gpg: /tmp/update-manager-bpIptI/trustdb.gpg: trustdb created gpg: Good signature from "Ubuntu Archive Automatic Signing Key " gpg: WARNING: This key is not certified with a trusted signature! gpg: There is no indication that the signature belongs to the owner. Primary key fingerprint: 6302 39CC 130E 1A7F D81A 27B1 4097 6EAF 437D 05B5 gpg: Signature made Fri 28 Sep 2012 03:55:55 AM IST using RSA key ID C0B21F32 gpg: Can't check signature: public key not found Traceback (most recent call last): File "/usr/lib/python2.7/dist-packages/UpdateManager/UpdateManager.py", line 1110, in on_button_dist_upgrade_clicked fetcher.run() File "/usr/lib/python2.7/dist-packages/UpdateManager/Core/DistUpgradeFetcherCore.py", line 253, in run _("Authenticating the upgrade failed. There may be a problem " File "/usr/lib/python2.7/dist-packages/UpdateManager/DistUpgradeFetcher.py", line 41, in error return error(self.window_main, summary, message) File "/usr/lib/python2.7/dist-packages/UpdateManager/Core/utils.py", line 384, in error d.window.set_functions(Gdk.FUNC_MOVE) RuntimeError: unable to get the value gpg: /tmp/tmplqoLDu/trustdb.gpg: trustdb created