I have installed Ubuntu 12.04 LTS two weeks ago by downloading the iso image, creating a startup usb stick from this image, booting the live system and finally installing. I have been working successfully during these two weeks in order to get everything I need up and running. :-)
Since most of the software needed is properly working I decided to tell the update-manager to look for packages to update. After downloading the package information the update-manager says (1) "The software on this computer is up to date. The package information was just updated". However, immediately after this, a second dialog pops up and says (2) "Not all updates can be installed. Run a partial upgrade, to install as many updates as possible". If the software is up to date, there should be nothing to install, so (2) contradicts (1).
Choosing the offered "Partial Upgrade" results in (3) "Upgrading over remote connection not supported. You are running the upgrade over a remote ssh connection with a frontend that does not support this. Please try a text mode upgrade with 'do-release-upgrade'." Finally, launching do-release-upgrade on the console (e.g. Ctrl-Alt-F5) reports (4) "Checking for a new Ubuntu release. No new release found." Since (4) supports (1), it does not matter if upgrading by means of a remote connection is supported (3).
Please give me a hint how to get the update-manager properly working. I can't tell, if my installation is complete and up to date or if there are package updates available, I should install but my package management has an aching stomach.