sudo apt-get update error: E: Splitting of file /var/lib/apt/lists/si.archive.ubuntu.com
You can use
sudo rm /var/lib/apt/lists/*
in order to remove all the lists and
sudo apt-get update
to download the lists again
This just happened on my system too, and the reason was my /tmp disk was full.
After removing some files from /tmp, apt-get update started working again.
I also added a bug report at Launchpad