Upgrade hangs on ttf-mscorefonts-installer

I've got the exact same issue, the upgrade hung off while downloading ms-core-fonts from sourceforge. After 2 hours waiting for the process to continue, I decided to kill the process downloading the package.

So I just ran "sudo htop" then F5 to see the tree of process, I started from the main process responsible for the upgrade to precise and searched for the one reponsible for the download. I killed this one, then the process skips the ms-core-font download part then continues and finishes the updrage to precise.

If you don't have the htop, just try ps -ejHf and find the package-data-downloader and kill it.

root     29696 11731 29696 29696  0 22:46 pts/2    00:00:04           /usr/bin/dpkg --force-overwrite --status-fd 56 --configure dmsetup libdevmapper1.02.1 libfreetype6 g
root     22330 29696 29696 29696  0 23:02 pts/2    00:00:00             /bin/sh /var/lib/dpkg/info/update-notifier-common.postinst configure 0.117ubuntu3.2
root     22332 22330 29696 29696  0 23:02 pts/2    00:00:00               /usr/bin/python /usr/lib/update-notifier/package-data-downloader

I had the same issue with ttf-mscorefonts-installer when upgrading to 16.04 from 14.04. I tried killing processes related to ttf-mscorefonts-installer via htop (both SIGTERM and SIGKILL) which did not work for me. I did some further digging and found that I had neglected to hit the Tab, which highlights OK and allows the Enter key to continue the process as outlined here. I felt pretty stupid until I realized that it would have been extremely simple to include the words "Hit tab and then enter to accept" on the page that requests acceptance. I have no doubt that making this small adjustment would eliminate a great deal of frustration.

You could remove the package and then reinstall it when you have the rest of the system upgraded, I suppose. It is not supposed to fail while downloading the fonts, of course, but if source forge is down for you right now, it might be a workaround option.