Recently I had a problem with the update-manager and search for a solution. On my search I found a post, where someone had the same problem and as solution they told him he should run this command on the terminal:
sudo rm /var/lib/apt/lists/*
I also run this, and the update-manager worked again. But now, I noticed that apt-get won't install anything. I wanted to install rvm (for ruby) and therefore I needed a few packages (build-essential and curl to be precise). But if I tried to install them, I always get the message that there is no installcandidate for that package... . What can I do to get apt-get working again?