Ubuntu lets you build/compile a package from source using the apt-build utility. The latter does not ship by default on standard Ubuntu installs. You may install it as follows:
sudo apt-get install apt-build
Now, to compile a package from source, you do the following:
sudo apt-build install package_name
However, since a few days that I'm using apt-build on Ubuntu 14.04 LTS I noticed an error showing up every time I update the software repositories list.
Upon searching I found that the bug has been around since a while and affects 64bit systems. As few people might be using the apt-build feature therefore it hasn't been on a priority list. If you're using apt-build on a 64bit machine it's highly probable that you'll encounter the error too.
It can be fixed by specifying the architecture type in the repository configuration file. In this case it'll be the file /etc/apt/sources.list.d/apt-build.list.
Replace the following line:
deb file:/var/cache/apt-build/repository apt-build main
deb [arch=amd64] file:/var/cache/apt-build/repository apt-build main
That should do the trick. You can now run sudo apt-get update without errors showing up.
The bug is being tracked here.