I've been experimenting with Ubuntu 10.04(64bit) inside a VirtualBox VM. This isn't my first experience with Linux, but I'm still very much a Linux noob. Whenever I try to install software from the Ubuntu Software Center, the installation gets interrupted and I get a warning that this installation requires untrusted sources. I can install anything I want using apt-get, it's just the gui that doesn't work. I've done research on the issue and taken the following precautions with no result: under software sources Allowed Canonical partners Allowed source code Changed the download source to main server I get no errors when running an apt-get update. Can anyone shed some light on the issue?