So, I decided I would stick with 12.04 for now, instead of upgrading to 12.10, but for some reason, I cannot install updates anymore. When I check the Update Manager, I get a message saying that "Not all updates can be installed", and that I should run a partial upgrade. When I click that box and enter my password, I see a distribution Upgrade window. The problem is, I just want to install the usual security patches and bug fixes, not a new operating system! What should I do?

(Also, I'm running 64 bits)