Hi 
Using Linux for a time ,in its very essence one of the errors I often come across with is downloading problem for certain add-ons.

If you get the following error: 

Failure to download extra data files

The following packages requested additional data downloads after package installation,
but the data could not be downloaded or could not be processed.

ttf-mscorefonts-installer

The download will be attempted again later, or you can try the download again now.
 Running this command requires an active Internet connection.  

So this certain packet actually stands for Microsoft‘s font files freely available from the Microsoft for you to use and download without sharing with any 3rd party or individual.Therefore, there is a probable connection problem that you must have had when you attempted to download it.

To fix it: 

sudo apt-get remove --purge ttf-mscorefonts-installer
sudo apt-get install ubuntu-restricted-extras
     

Sincerely,Ahmet