Dynamic images are broken on the front and back end across a network - one obvious place, the previews in the media manager are not working.
Looking at the image paths I see :
This is missing the account name and does not work - it should be: http://wpmudomain.com/accountname/files/2014/02/somefile.jpg
I'm not sure what triggered this.
I'm assuming there must be a db setting somewhere that has gotten confused?